Glossary of Automotive Terms – O

Letter O – Dictionary of Automotive Terms

Abbreviation for Oxygen
Abbreviation for Oxygen Sensor Signal (Bank 1)
Abbreviation for Oxygen Sensor Signal (Bank 2)
O2 sensor
A detection device that monitors the amount of oxygen in the exhaust stream and sends that information the ECM. Also called an Oxygen sensor or an Exhaust oxygen sensor

Abbreviation used by car dealers to indicate on approval of credit.
Untwisted fibers of old rope treated with a composition of resin and pitch, used to fill seams of wooden decks.
Abbreviation for Ford Motor Company Online Automotive Service Information System
Abbreviation for Order bill of lading. A shipment that is released to the consignee only when the original copy is paid for and payment is obtained by the driver prior to release of the shipment.
  1. Abbreviation for On-Board Diagnosis
  2. Abbreviation for On-Board Diagnostics
Abbreviation for On Board Diagnostics Version I
Abbreviation for On-Board Diagnostic system — second series.
OBD II Drive Cycle
An OBD II Drive Cycle is an extended set of driving procedures that takes into consideration the various types of driving conditions encountered in real life. These conditions may include starting the vehicle when it is cold, driving the vehicle at a steady speed: (cruising), accelerating, etc. An OBD II Drive Cycle begins when the ignition key is turned ‘On’: (when cold) and ends when the vehicle has been driven in such a way as to have all the Enabling Criteria met for all its applicable Monitors. Only those trips that provide the Enabling Criteria for all Monitors applicable to the vehicle to run and complete their individual diagnostic tests qualify as an OBD II Drive Cycle. OBD II Drive Cycle requirements vary from one model of vehicle to another. Vehicle manufacturers set these procedures. Consult your vehicle’s service manual for OBD II Drive Cycle procedures. Do not confuse a ‘Trip’ Drive Cycle with an OBD II Drive Cycle. A ‘Trip’ Drive Cycle provides the ‘Enabling Criteria’ for one specific Monitor to run and complete its diagnostic testing. An OBD II Drive Cycle must meet the ‘Enabling Criteria’ for all Monitors on a particular vehicle to run and complete their diagnostic testing.
Abbreviation for On Board Diagnostic System Status
OBD system
The entire purpose of the OBD system is the control and reduction of pollutants: The two gases Carbon Monoxide: (CO) and Nitrous Oxide: (NOx), and unburnt Hydrocarbons: (HC). The absolute imperative for the OBD is to control these substances within fine limits and to protect the catalyst(s) from damage. In order to achieve this if necessary it will sacrifice engine performance.
A journey during which all OBD tests have been completed.
Oblique crash test
You have seen crash tests where the vehicle slams into a brick wall, but what happens if your vehicle is hit on the front corner. Do you still have the same kind of protection? The oblique crash test determines a vehicle’s ability to withstand crashes which may occur to any of its four corners.
Abbreviation for or best offer which indicates that the seller is willing to negotiate. If you offered $10 for a vehicle and you were the only one who made an offer, technically your offer is the best. However most sellers understand $3000 obo as meaning about $3000, maybe less. Some think it means ‘I’ll sell it for $3000; but if someone offers $4000, I will take that instead.’
OBO ship
Abbreviation for Ore-bulk-oil carrier. A multipurpose ship that can carry ore, dry bulk goods, and oil.
Abbreviation for or best reasonable offer.
Obsolete Stock
Product that has no useable purpose that remains in the warehouse.
Obstruction wrench
Obstruction wrench
Obstruction wrench
A bent ring wrench for reaching around manifold and other obstacles to work on parts with difficult access, such as starters or alternators
  1. Abbreviation for Overhead camshaft.
  2. Abbreviation for Oxidation catalyst
  3. Abbreviation for Oxidation Catalytic Converter

  1. Abbreviation for Output Circuit Check (Ford)
  2. Abbreviation for output cycling check
Ocean container
Ocean container
Ocean Container
A completely enclosed, often water tight container designed to be loaded onto ocean freighters to carry commodities overseas. Also called a sea can.
Ocean liner blast horn
A horn which imitates the deep bellow of an ocean liner horn
Abbreviation for Office of Consolidated Emergency Management.
Abbreviation for Overdrive Cancel Indicator Lamp
  1. Abbreviation for Overdrive Cancel Switch
  2. Abbreviation for Outer Continental Shelf
Abbreviation for Octane Adjust Fuel Switch
Octagonal bolt
A bolt with an eight-sided head instead of the standard six-sided head
Octagonal head bolt
A bolt with an eight-sided head
Octagon nut
A nut with eight sides instead of the standard six sides.
A flammable liquid hydrocarbon found in petroleum. Used as a standard to measure the anti-knock properties of motor fuel.

Octane Enhancer
Any substance such as MTBE, ETBE, Toluene, and Xylene that is added to gasoline to increase octane and reduce engine knock.
Octane number
Every brand of gasoline has an octane rating or number which indicates its ability to resist knocking. When the numbers were first developed, the researchers found that normal heptane (a Hydrocarbon) had almost no ability to resist knocking so they gave it an octane number of zero. Then they found that isooctane (also a Hydrocarbon) was very resistant to knocking so they gave it the octane number of 100. To measure a particular sample of gasoline they discovered when it began to create Detonation. Then they mixed isooctane to heptane to find out what percentage of isooctane created the same results as the sample of gasoline. In United States, there are two methods for determining the octane number depending upon operating conditions. The Research Octane Number (RON) is obtained when conditions are somewhat mild. The Motor Octane Number (MON) is obtained when conditions are somewhat severe and give a much lower number than the RON. The numbers on the gasoline pumps are usually an average of the RON and MON. Usually the pump number is about four numbers less than the RON. Thus if the automobile manufacturer recommends using gasoline with a RON of 91 or more, it would be acceptable to use pump gas rating of 87. The pump number is the Anti-knock index which is half the sum of the RON and the MON.

Octane rating
A number used to indicate gasoline’s antiknock performance (i.e., self ignition) in motor vehicle engines. The two recognized laboratory engine test methods for determining the antiknock rating, i.e., octane rating, of gasolines are the Research method and the Motor method. To provide a single number as guidance to the consumer, the antiknock index (R + M)/2, which is the average of the Research and Motor octane numbers, was developed. Engines with higher compression ratios require higher octane gasoline.

Frequency difference between harmonic vibrations; the doubling of the frequency of sound.
Octyl alcohol-ethyl hexanol
Additive in absorption machines that reduces surface tension in absorber.
  1. Abbreviation for Outside diameter
  2. Outer diameter
  3. Overdrive
Abbreviation for Output Device Monitor
An instrument which measures and registers the number of kilometres or miles a vehicle travels. In automobiles, it is usually located in the same housing as the speedometer. Bicycles do not generally come with odometers as standard equipment. Motorcycles usually have the odometer in an instrument housing along with the speedometer for measuring and registering the miles and tenths of a mile (or kilometres and tenths of a kilometre) that the vehicle is driven. Some cars and motorcycles also have an additional trip odometer that can be reset to zero for conveniently measuring the miles or kilometres driven during trips or between fuel fillups.
That property of air contaminants that affect the sense of smell.
Abbreviation for Overdrive Drum Speed
Abbreviation for Original equipment.
Abbreviation for Organization for Economic Co-operation and Development.
Abbreviation for original equipment manufacturer. Products or parts supplied by the company which first created or produced them. Contrasts with aftermarket parts which are similar to OEM, but made by a different company.
OEM Standard
The criteria established by the original manufacturer for a particular part or product. Often aftermarket parts includes a statement such as ‘meets or exceeds OEM Standard’ to indicate that the product is reliable.
The unit of magnetic field strength in the centimeter-gram-second electromagnetic system of units, equal to the field strength at the center of a plane circular coil of one turn and one centimeter radius, where there is a current of 1/2 abampere in the coil. An abampere is 10 times an ampere.
Abbreviation for Oxygen to Fuel ratio
The condition that exists when a turbocharger is not producing power. If exhaust pressure is not sufficient to spin the turbine, the turbocharger goes off boost.
Off-car balance
A procedure of removing a wheel from a vehicle and balancing the assembly. This is the most common form of wheel balancing and is done either statically or Dynamically. The preferred method of off-car balancing is dynamic.
Off color
A color mismatch (though very close to the correct color) due to wrong paint mixing or application
Off cycle
Segment of refrigeration cycle when system is not operating.
Offer up
To bring a part close to or in contact with another, ready to fit the pieces together
Off-highway use
Includes petroleum products sales for use in:

  • Construction equipment including earthmoving equipment, cranes, stationary generators, air compressors, etc.
  • non-Construction equipment such as logging
  • But not farm use of petroleum — instead see Farm use
Off-highway vehicle
Vehicle intended for operation on unmade surfaces or rough terrain (i.e., for construction or agriculture).
Office of Mobile Sources
Division of EPA that proposes, promulgates and enforces regulations to control emissions of NAAQS pollutants and precursors from motor fuels and vehicles.
Office of Motor Carriers
(OMC) an interstate heavy truck and bus regulatory agency.
Off-idle Air Bleed
Off-idle discharge ports
The holes that deliver fuel from the idle circuit during the transition from curb-idle to the main metering circuit. Located just above the throttle plates. At curb idle, off-idle ports function as an extra air bleed for further emulsification of the idle mixture; but as vacuum moves up the carburetor bore when the throttle plates are opened, they become fuel discharge ports. Either one or more holes, or a single slot (slots are usually used because they are cheaper to manufacture). Also called Transfer ports
A vehicle which was once leased, but now has been returned after the lease has expired.
Something that is independent of the main production process line which is characterized by a separate operation
Off-line painting
The painting of parts, mostly plastic parts, outside the actual painting line
Off ramp
Off Ramp
Exit slip road. A road that veers off to one side of a highway to go onto another road. Opposite to on ramp.
Off-Road Bicycle Association
Off-road tire
(OTR) A tire that is used on vehicles designed for operation on unmade surfaces or rough terrain (i.e., for construction or agriculture or recreation).


Off-road vehicle
Vehicle intended for operation on unmade surfaces or rough terrain (i.e., for construction or agriculture).
Off-route points
Destination locations that are not on the regular route highways of line-haul carriers, generally served only on irregular schedules.
  1. Something set at an angle or to one side.
  2. The Scrub radius.
  3. The distance between the centerline of the rim and the attachment face of the wheel disc at the wheel hub; this dimension can either be positive, negative, or zero. An important measurement for positioning the tire to insure proper tracking of the vehicle and adequate dual spacing.
Offset angle
The angle of the offset crankpins in V-engines
Offset crankshaft
A crankshaft layout whereby the axes of the crankshaft and the piston pin do not intersect. They do not intersect because the forces acting on the piston do not act uniformly on the walls of the cylinder through the skirt of the piston but much more on the side affected by the thrust of the con red during the power stroke. The crankshaft is thus offset, so that the con rod is less inclined during the power stroke than during the compression stroke
Offset dish
A wheel with a hub which is not in the same plane as the rim.
Offset handle
A drive handle for use with sockets, with one end set at 90° to the handle
Offset link
Offset linkOffset link

A link in a chain which is often called a half-link. An offset link increases the number of links by one. Thus it is used when an uneven number of links in the total strand is required.

Offset open-end wrench
offset screwdriver
Offset screwdriver
Offset screwdriver
A screwdriver with either straight or Phillips (cross-head) tips or a combination of both, and the two ends set at right angles to the shank, somewhat in the shape of the letter Z
Offset Section
For a roller chain, a factory-assembled section, made up of a roller link and an offset link. Offset sections are used to connect strands of chain having an odd number of pitches.
Offset steering
Offset twin
A typical motorcycle engine with the two crankpins offset by 180°
Offset wrench
Offset wrench
Offset wrench
An L-shaped tool for turning recessed screws
Off shade
A color mismatch (though very close to the correct color) due to wrong paint mixing or application
(o/s) The side of the vehicle farthest away from the curb (when driving)
Off-the-car balancing
Balancing the wheel after it has been removed from the car. The opposite is On-the-car balancing
Off-the-dolly panel beating
A metalworking technique used to hammer out dents in the bodywork. If the panel has a depression on one side, the dolly is held behind the depression, and the hammer blows are directed on the ridge away from the dolly, i.e., on the other side of the dolly. This causes a reaction by the dolly, producing an alternating impact on the dent from both sides
Abbreviation for Overhead camshaft.
  1. A unit of measurement used to indicate the amount of resistance to the flow of electricity in a given circuit.
  2. Unit of measurement of electrical resistance. One ohm exists when one volt causes a flow of one ampere.
Ohmic polarization
Losses created by the resistance to the flow of ions in the electrolyte and resistance to flow of electrons through the electrode and bipolar plate materials. Because both the electrolyte and fuel cell electrodes obey Ohm’s law, the ohmic losses can be expressed by the equation Ohm = iR
An instrument used to measure the amount of electrical resistance in a given unit or circuit (in ohms).
Ohm’s law
Mathematical relationship between voltage, resistance, and amount of current in an electrical circuit. It states E=I x R; I=E/R; R=E/I
Abbreviation for Overhead valveValve-in-head engine in which the valves are directly above the piston.
OHV engine

Abbreviation for Organisation Internationale des Constructeurs d’Automobiles (i.e., International Organization of Motor Vehicle Manufacturers)
A substance that lubricates and cools the moving parts of the engine and reduces the formation of rust and corrosion. It contains additives which fights the corrosion of bearings, keeps small particles in suspension, reduces engine wear, and reduces oxidization, minimizes carbon, Lacquer, and gum formation. Oil comes in varying Viscosity weights suitable for efficient operation in cold and hot weather and for engines in varying states of wear. A mixture of hydrocarbons usually existing in the liquid state in natural underground pools or reservoirs. Gas is often found in association with oil.

Oil additive
Any one of a variety of chemicals added to engine oils to improve their performance. They include additives to increase viscosity at high and low temperatures; to inhibit corrosion, wear, and foaming; to prevent the formation of breakdown products caused by oil oxidation and to keep these in suspension
Oil and water extractor
Oil bath air cleaner
An Air cleaner that uses a pool of oil to insure the removal of impurities from the air entering the carburetor.
Oil bath suspension
A suspension fork design that fills the lower part of the fork with oil, allowing the oil to be used for both damping and lubrication.
Oil binding
Condition in which oil layer on top of refrigerant liquid may prevent it from evaporating at normal pressure and temperature.
Oil bleed line
An external oil line which circumvents the evaporator pressure regulator or bypass valve to ensure positive oil return to the compressor when rpm are high and the system is under a low charge or clogged
Oil bleed passage
An internal orifice which bypasses the evaporator pressure regulator, the bypass valve or the expansion valve to ensure positive oil return to the compressor
Oil breather
Ventilated cap on oil filler pipe for allowing fumes to escape from the crankcase.
Oil breather pipe
A crankcase breather pipe used prior to engine emission control systems to remove fumes and pressure from the engine crankcase. Also called Road-draft tube. The tube, which was connected to the crankcase and suspended slightly above the ground, depended on venturi action to create a partial vacuum as the vehicle moved. The method was ineffective below about 20 mph
Oil breather tube
Oil burner
An engine that consumes an excessive quantity of oil.
Oil can
  1. A container with a long, thin nozzle for lubricating machinery.
  2. A shallow dent in a panel that causes the panel to warp. The dent will spring back into its original shape with a characteristic sound if light pressure is applied but will not retain its normal shape once the pressure is released. It must therefore be straightened with body tools
Oil change
The act of draining and replacing the engine oil at regular intervals
Oil circulation
The passing of oil throughout the engine. The engine oil circulation is maintained by a gear-type pump with an output of up to 35 litres per hour
Oil-combination splash and pressure system
An engine oiling system that uses both pressure and splash oiling to accomplish proper lubrication.
Oil consumption
The amount of oil an engine uses
Oil control orifice valve
A valve located in the feed line between cylinder and cylinder head
Piston rings
Click to supersize Piston rings
Oil control ring
A piston ring designed to scrape oil from the cylinder wall, the ring is of such a design as to allow the oil to pass through the ring and then through holes or slots in the groove. In this way the oil lubricates the cylinder walls and is returned to the pan rather than getting into the combustion chamber where it might foul the spark plugs and create carbon on the head of the cylinder. There are many shapes and special designs used on oil control rings. Often it is the third or fourth ring from the top. Also called Oil scraper ring.
Oil cooler
This looks like a small radiator used to cool off the engine oil or the Automatic transmission fluid. As air passes through the cooler, the temperature of the oil in the cooler is reduced. Some units reduce the temperature of the manual Gearbox and Differential lubricants in racing cars.
Oil cooler bypass valve
An oil-temperature-controlled valve which closes the oil circuit through the oil cooler when the oil is still cold; similar function as the thermostat in the engine cooling system. Engine oil is heated to a considerable temperature in engines subject to a high thermal load. This in turn greatly reduces the lubricating ability and the cooling capacity of the oil. Thermostats control the oil volume to the oil cooler, thus ensuring constant temperature of the oil
Oil dipstick

Oil Distillation
Oil drain plug
The large bolt or plug that secures the drain hole in the Oil pan. It is sometimes fitted with a Gasket or O-ring to prevent leakage. Often the drain plug is magnetized so that any stray particles of iron will stick to it rather than lodge in some vital orifice. Also called sump drain plug
Oil drain valve
A valve in an upright oil filter housing which lets oil drain into the oil pan when the filter element is removed. It prevents oil spill
Oil duct
A pipe or passage through which oil flows under pressure. Also called oil passage or oil way.
  1. A Cam lubricator.
  2. An Oil can
Oilfield Body
Heavily constructed platform-type body equipped with instruments and machinery for oil drilling.
Oil filler cap
A cap covering the Oil filler hole
Oil filler hole
A hole at the top of the engine (usually in the rocker cover) through which new oil can be added after the Oil filler cap is removed.
Oil filter
Oil filterOil filter

A device used to strain the oil in the engine thus removing abrasive particles. Some filters are a can-like container, others look like small Air filters which fit into a Canister. Most manufacturers recommend that the oil filter should be replaced at least every second oil change.

Oil filter bypass valve
A valve in or near the oil filter which routes the oil unfiltered directly to the lubricating points; it comes into operation when the oil filter is clogged so that pressure across the filter is higher than the pressure needed to overcome the oil filter bypass valve spring
Oil filter cartridge
  1. The type of oil filter usually used on automotive engines which comes complete with filter and housing, and where both components are replaced together.
  2. A paper or textile insert for the oil filter housing (quite commonly used on motorcycle engines where e.g., the main filter is a disposable cartridge, while a filter screen is located on the bottom of the oil pump)
Oil filter hole
The opening in the engine block to which the oil filter is secured.
Oil filter housing
A case surrounding an oil filter
Oil filter wrench
Filter wrenchFilter strap wrench

A special automotive tool for the removal and installation of oil filters; it comes in a variety of shapes, e.g., as a strap wrench, chain wrench, spider filter wrench, or cap wrench,

Oil flag
Oil flagOil flag

Also called surface flag, this indicates there is a problem with, or change in, the surface ahead. This commonly means there is oil on the track. It also can mean water or another substance causing a change in the racing surface. The number of stripes on this flag varies (some are yellow with two red stripes) but the meaning remains the same.

Oil full pressure system
Oil-full pressure system
An engine oiling system that forces oil, under pressure, to the moving parts of the engine.
Oil gage

Oil gallery
A pipe or drilled passageway in the engine that is used to carry engine oil from one area to another.

Oil gauge
An instrument on the dashboard which indicates the oil pressure as the oil is pumped through the engine. If this gauge shows a sharp drop, reads low, or lights up, it is possible that there is no oil in the engine. Stop the vehicle and turn off the engine. Check the oil level and replenish it as necessary. A vehicle with no oil in the engine could destroy an engine within a kilometre (or a mile). Also called Oil pressure gauge
Oil grade
A rating of an oil according to its viscosity
Oil groove
Recess designed to either accommodate or transport lubricant
Newer, air-and-oil-cooled BMW Boxer engines
Oil-immersed clutch
Oiling splash system
Method of lubricating moving parts by agitating or splashing oil in the crankcase.
Oilless bearing
A sleeve bearing of porous material that depends solely on the porosity of the metal to store oil.
Oil level
The depth of oil in the oil pan, gearbox, transmission, power steering reservoir, or rear axle.

Oil level gauge
A dial on the instrument panel that indicates the oil level; operates when the ignition is switched on and stops shortly after the engine starts to run
Oil level sensor
A detection device mounted in the oil pan that supplies information on the engine oil level to the corresponding gauge
Oil level warning light
Oil life monitor
A vehicle computer that lets you know when to change the engine oil. This is not based on mileage, but on engine revolutions and operating temperature. Never drive your vehicle more than 16,000 kilometres or 12 months without an oil and filter change.
Oil lubrication
Engine oil designed for light duty service under favorable conditions.
Engine oil designed for moderate duty service with occasional high speeds.
Engine oil designed for high speed, heavy duty operation or for a great deal of stop and go driving.
Oil pan
The removable metal chamber or bowl (usually of sheet steel or cast alloy) at the bottom of the crankcase into which the oil drains to be stored. The Oil drain plug is found at the bottom of this pan and can be removed to allow the old oil to flow out of the vehicle during an oil change. The British term is sump.
Oil pan drain plug
Short fat bolt for draining the sump (when removed)
Oil pan gasket
A gasket fitted between the cylinder block and the oil pan
Oil pan guard
A shield fitted under the engine to protect the oil pan
Oil passage
A pipe or passage through which oil flows under pressure. Also called oil duct or oil way
Oil pick-up
A pipe or tube from the strainer to the oil pump in the oil pan
Oil pick-up pipe
A pipe or tube from the strainer to the oil pump in the oil pan
Oil pressure
The lubrication points of the engine will be lubricated sufficiently only if, in addition to the oil quantity required, the oil pressure is also sufficient; the oil pressure is maintained by the oil pump
Oil pressure gage
Oil pressure gauge
An instrument on the dashboard which indicates the oil pressure as the oil is pumped through the engine. If this gauge shows a sharp drop, reads low, or lights up, it is possible that there is no oil in the engine. Stop the vehicle and turn off the engine. Check the oil level and replenish it as necessary. A vehicle with no oil in the engine could destroy an engine within a kilometre (or a mile).
Oil pressure safety cutout
Motor protection device that senses oil pressure in the compressor. Is wired in series with the compressor and will shut it off during periods of low oil pressure.
Oil pressure sensor
A detection device mounted above the oil filter that supplies information on the engine oil pressure to the corresponding warning light
Oil pressure switch
A switch which indicates a drop to below the minimum permissible oil pressure by illuminating the Oil pressure warning light
Oil pressure warning light
An instrument panel light that illuminates when oil pressure falls below a certain level
Oil pump
The device located in the crankcase used to force oil, under pressure, to various parts of the engine, it is driven by a gear on the camshaft. There are two types Gear-type oil pump and Rotor-type oil pump.
Oil pumping
A condition where an excessive quantity of oil passes the piston rings and is consumed in the combustion chamber.
Oil pump strainer
A coarse-mesh metal screen on the bottom of the pick-up pipe that prevents foreign matter (such as lost washers, nuts and bolts) from entering the Oil pump
Oil rail
The part of the oil ring responsible for the seal between piston and cylinder wall and thus for the actual scraping off of the oil
Oil, refrigeration
Specially prepared oil used in refrigerator mechanism which circulates, to some extent, with refrigerant.
Oil reservoir
An underground pool of liquid consisting of hydrocarbons, sulfur, oxygen, and nitrogen trapped within a geological formation and protected from evaporation by the overlying mineral strata.
Oil ring
The lowermost piston ring that scrapes off excess oil from the cylinder walls and returns it to the Oil pan via vents in the ring and piston. The oil ring consists of up to three separate pieces. The two outside pieces are thin rings (rails), and the inner section of the ring is called the expander ring. The oil ring is also called the oil scraper ring or oil control ring
Oil scraper ring
Oil screen
Oil seal
A device used to prevent oil leakage past a certain area.

Oil sensor
A detection device which recognizes when the oil pressure or oil level is too low
Oil separator
  1. A wire-mesh filter used to trap oil in the fumes drawn out of the engine by the crankcase ventilation system
  2. Device to separate refrigerant oil from refrigerant gas and return the oil to compressor crankcase.
Oil slinger
A cone-shaped collar attached to a revolving shaft so that any oil passing that point will be thrown outward where it will return to the point of origin.
Oil splash system
Oil-splash system
An engine oiling system that depends on the Connecting rods to dip into oil troughs and splash the oil to all moving parts.
Oil sludge
A thick deposit in the oil pan and elsewhere, of dirt and the products of combustion, partial combustion and oxidation of the oil (e.g. carbon particles, unburned hydrocarbons and oxides)
Oil sump

Oil tanker
A ship designed for transporting oil in bulk
Oil temperature gauge
A gauge which indicates the temperature of the engine oil
Oil thermal vacuum switch
(OTVS) a switch used by some GM vehicle to shut off vacuum to the early evaporation (EFE) valve when oil temperature reaches 150° F
Oil trap
Oil way
A pipe or passage through which oil flows under pressure. Also called oil duct or oil passage
Abbreviation for Open Loop
Click image for books on
A vehicle brand from General Motors of which the 1949-50 88 Coupe, Convertible, and Holiday are milestone cars. The 1949 98 Holiday Hardtop is a milestone car. The 1953 Fiesta is a milestone car. The 1964-70 442 models are milestone cars. Other models include

Class of unsaturated paraffin hydrocarbons recovered from petroleum. Typical examples include: butene, ethylene and Propylene.
The main structural member of the support assemblies of an aircraft’s landing gear.
Oleopneumatic suspension
Abbreviation for operation and maintenance
Abbreviation for Office of Motor Carriers an interstate heavy truck and bus regulatory agency.
Oldsmobile Omega
Click image for books on Oldsmobile Omega
A model of automobile manufactured by the Oldsmobile division of General Motors
On-board computer
  1. An electronic component used to control vehicle electrical circuits, etc. and to process data for instrument panel gauges
  2. A cab-mounted device on a truck which electronically or mechanically records data such as truck speed, engine rpm, idle time and other information useful to trucking management. Also called Trip Recorder
On board diagnostics

  1. A unit that monitors the Electric Control Unit and system responses for errors during normal vehicle operations. When the vehicle is serviced, this information on the errors can be down loaded and displayed to the service personnel which will facilitate the trouble shooting process.
  2. A system on board of the vehicle that monitors emission control components and alerts the driver (e.g., by an instrument panel light) if malfunctions or emission deterioration occurs. The OBD system involves a number of sensors and a data processor, which is typically integrated with the vehicle’s electronic management system.
On-board diagnostic system (OBD) and (OBDII)
  1. An indicating device on the car that alerts the driver when something is wrong in the system
  2. A system which monitors some or all computer input and control signals. Signal(s) outside predetermined limits implies a fault in the system or in a related system
Onboard Refueling Vapor Recovery
(ORVR) System required on vehicles beginning in 1998 to control refueling emissions.
On boost
The condition that exists when a turbocharger is producing power. When exhaust pressure is sufficient, the turbine spins, and the turbo is on boost.
On-car balance
In contrast with off-car balancing (which removes a wheel from the vehicle) on-car balancing leaves the wheel on the vehicle and a special machine is used to balance the tire, wheel and brake assembly making adjustment for all of these components. Obviously this is the best (and most costly) procedure in obtaining balance.
On-center feel
The responsiveness and feel of the steering when the wheel is approximately centered. In a car with good on-center feel, the steering wheel tends to return to center when slightly deflected, assisting straight-line Stability.
One-coat finish
A finish consisting of a single coat of paint
One eyed monster
Slang for a T.V. set as in ‘I think my kids would die if the one-eyed-monster broke.’
On-foot recce
Inspecting a difficult off-road obstacle on foot before committing your vehicle to it.
One-groove track
Regardless of the width of a track, going into and coming out of a tight turn causes the track to have room for only one line of race cars rather than two.
A car or spare part of which only a single unit is made
One off
A car or spare part of which only a single unit is made
One-piece rim
A wheel rim consisting of one part, designed for tubeless tire mounting. The opposite is a Multi-piece rim
One-piece rim designation
A coded description of a one-piece wheel rim.
One-piece wheel
A wheel with a rim constructed in one piece incorporating a well formation at or near its center to enable the tire beads to be mounted over the rim flanges. A cast wheel, a one-piece forged wheel, and a steel wheel have either a 5° drop center rim, 15° drop center rim, wide base rim, or double wide base rim are one-piece wheels. The opposite is a Multi-piece wheel
One price selling
Published fixed price displayed on a new vehicle eliminating need for negotiation.
One sun
Natural solar insulation falling on an object without concentration or diffusion of the solar rays.
One way
One-way sign
A directional sign indicating that traffic must proceed in the direction of the arrow.

One way clutch
A mechanical clutch which transmits power in one direction of rotation only; when torque is not applied, the driven member rotates freely; used in automatic transmissions and the old freewheel.

One-way clutch
One way screw
One way screw
One-Way Head Screw
A round head screw which is slotted but has side clearances at diagonally opposite sides of the slot so that the screw can be driven only in the direction of assembly, designed for preventing tampering.
One-way valve
On-highway use
Includes sales of fuel for use in motor vehicles. Volumes used by companies in the marketing and distribution of petroleum products are also included.
A state in which a piece of equipment or subsystem is directly connected with or incorporated into the main system
On-line painting
A painting of components within the actual painting line. This is especially relevant for plastic moldings, which are fitted to the metal car body after the welding assembly operation. On-line painting means that such plastic parts are painted together with the body and must withstand the bake-in temperatures of about 150°C
Abbreviation for or nearest offer as a term of negotiation which indicates that the seller is not too flexible in his price.
On/off delay
On Ramp
On Ramp
Entry slip road. A road that joins a main highway by merging.
OnStar is the innovative communication service from General Motors that combines Global Positioning System satellite technology and a hands free voice activated cellular phone, linking the driver and the vehicle to the OnStar Center 7 days a week, 24 hours a day where advisors provide real-time, person to person assistance.
On-the-car balancing
Balancing the wheel while it is still attached to the car. The opposite is Off-the-car balancing
On-the-dolly panel beating
A metalworking technique used to tap out dents in the bodywork. The dolly is held directly under the ridge in the panel so that the dolly contour closely matches that of the original panel shape. Hammering is then directed at the peak of the ridge, working along the ridge from end to end in a progressive manner to push the area down gradually to its original shape
On-the-road charges
Extra charges, in addition to the list price of a new car, to cover delivery, license, etc.
On the side
Trucker slang for pulled over on the shoulder as in, ‘You got a 4-wheeler on the side up ahead.’
Abbreviation for Open enclosure — a type of electric motor housing.
An instrument for measuring the content of particulate suspended in a fluid
Opaqueness or quality or state of a body which renders it impervious to the rays of light such as the density of exhaust smoke.

Abbreviation for Organization of the Petroleum Exporting Countries. An intergovernmental organization whose stated objective is to coordinate and unify petroleum policies among member countries. It was created at the Baghdad Conference on September 10-14, 1960, by Iran, Iraq, Kuwait, Saudi Arabia and Venezuela. The five founding members were later joined by nine other members: Qatar (1961); Indonesia (1962); Libya (1962); United Arab Emirates (1967); Algeria (1969); Nigeria (1971); Ecuador (1973-1992, 2007); Gabon (1975-1994) and Angola (2007).
Click image for books on Opel
A model of automobile manufactured by General Motors in Europe

Open bath
Open bevel
When two matching bevelled items are mated, they are ‘closed’ i.e., closed bevel. If the bevel in one does not match the other, they are open.
Open car
Another name for convertible
Open circuit
  1. A circuit in which a wire is broken or disconnected.
  2. Interrupted electrical circuit which stops flow of electricity.
  3. In an electric motor it is a defect that causes an interruption in the path through which the electrical current normally flows
Open circuit voltage
The voltage at device terminals when no appreciable current is flowing. Also called noload voltage.
When referring to street-legal sportbikes, open-class designates motorcycle with engines that displace more than 800 cubic inches of volume
Open coil glow plug
Open compressor
Term used to indicate an external drive compressor. Not hermetic.
Open cradle frame
A motorcycle frame without tubes running under the engine. The engine unit bolts into place between the front downtube and the swingarm pivot area as a semi-stressed or stressed member
Open-deck design
A design in which there is no metal at the cylinder head joint face between the cylinder walls and the outer block
Open differential
Common to all conventional motor vehicles, performing the basic drive axle differential function. Unlike a limited-slip or locked differential, an open differential is unable to compensate for traction distinctions from one side of the vehicle to the other, and will thus spin the wheel with the least available grip.
Open display case
Commercial refrigerator designed to maintain its contents at refrigerating temperatures even though the contents are in an open case.
Open drip-proof enclosure
An electric motor housing with normal insulation treatment which consists of one or more dips and bakes of varnish. The insulation system is composed of materials which will not absorb or retain moisture.

Open element glow plug
Open enclosure
(OP) An electric motor housing with ventilation openings in the end shields and/or shell to permit passage of cooling air over and around the windings. The locations of the openings not restricted. It is for use indoors, in fairly clean locations.


Open end lease
With an open-end lease, there is still a residual value set at the beginning of the lease. However, if the car is worth less than the residual value at the lease’s end, the lessee must pay the difference. In other words, the lessee assumes the risk for depreciation with an open-end lease.
Open-end wrench
A wrench with open jaws

Open face helmet
A motorcycle helmet which does not wrap around the chin to protect the whole face.
Open frame
A Step-through motorcycle/scooter frame
Opening angle
The angle of the timing diagram that indicates how long the port remains open
Opening cam/rocker
With Desmodromic engines, the cam/rocker responsible for opening the intake or exhaust valve
Opening Pressure
Open loop
  1. An operating condition or mode based on programmed instructions and not modified by a feedback system
  2. A predetermined operating condition not based on exhaust gas conditions.
Without feedback from e.g., oxygen-sensor control systems
Open-loop catalytic converter
A preset converter which does not use an oxygen-sensor control system and thus operates without feedback. The opposite is Computer-controlled catalytic converter. Certain engine management systems deactivate emission control systems (such as EGR and/or oxygen sensor control) under certain operating conditions (e.g., full-throttle driving); i.e., the electronic control module operates in the open-loop mode
Open-loop fuel control
  1. A non-feedback mode of operation which a feedback system resorts to when the engine is started while it is still cold. During this period, the oxygen sensor isn’t yet able to supply reliable data to the computer for controlling the air/fuel mix ratio because the engine isn’t yet warmed up. So mix control is handled by a program stored in computer memory
  2. System in which the air/fuel mixture is preset by design with no feedback correction signal to optimize fuel metering.
Open loop mode
Mode in which the computer operates without feedback from the oxygen sensor while the engine is in the cold running condition
Open loop system
A control system which operates by feeding in instructions at the beginning of a process and they are followed to complete the process.
Open refrigeration unit
Refrigeration in cabinets (units) without covers or with flexible covers made of plastic or some other material, hung in strips or curtains (fringed material, usually plastic, that push aside like a bead curtain). Flexible covers stop the flow of warm air into the refrigerated space.
Open registry
Open system
  1. Term for a crankcase emissions control system which vents to the atmosphere
  2. An anti-lock brake system in which the brake fluid released from the brakes during an ABS stop is not returned to the brake during the ABS stop but is stored in an accumulator
Open throttle
Open Throttle Switch
Open Top Van
A cargo body style vehicle with sides but without a permanent top–sometimes has a canvas cover.
Open tourer
Open type check valve
A valve, normally open to fluid flow in both directions, which closes when fluid flow in one direction exceeds a predetermined value.

Open type compressor
Compressor in which the crankshaft extends through the crankcase and is driven by an outside motor. Commonly called external drive compressor.
Open type system
Refrigerating system which uses a belt-driven or a coupling-driven compressor.
Open Washer
A washer with one side open so as to be removed or put under a nut without removing the nut.
Opera light
A light mounted on the outside of the B-pillar or C-pillar
Operated Absolute Valve
Operated Exhaust Heat Control Valve
Operated Power Booster
Operated window
Operating Authority
The entity responsible for a truck being on the road. Regardless of who owns the goods or who is driving the truck, the person or company who owns the truck transporting those goods is the operating authority and is responsible for the goods.
Operating costs
The costs of running a vehicle. It includes insurance premiums, tax, depreciation, fuel, oil, maintenance, repairs, etc.; usually expressed in dollars per mile or kilometre
Operating piston
A piston in an automatic transmission which causes its respective clutch(es), band, or multi-disc brakes to be applied by converting fluid pressure into mechanical force and movement
Operating Point
Operating pressure
  1. Actual pressure at which the system works under normal conditions. This pressure may be positive or negative (vacuum).
  2. Pressure at which a system is operating.
Operating profit
Pre-tax earnings after deducting all operating expenses from gross margin.
Operating valve
An operating valve is an automatic valve controlled by an operating control.
Operational test
A check of temperature, pressure, and other conditions under controlled circumstances to determine whether an air conditioner or some other system is operating optimally
Opera window
A small window on the rear quarter panel. It is usually circular.
Opportunity cost
The cost of what you didn’t do. For instance, if you have the cash to buy a car, the opportunity cost of the purchase is the interest lost on the cash you used for the car. One of the often-cited advantages of leasing is that it frees up your money to invest elsewhere.
Opposed engine
Opposed twin
A two cylinder engine where the cylindeers are horizontally opposed.
Opposite lock
The act of turning the wheels to avoid a Skid by steering in the opposite direction to which the vehicle is going. If the tail of the vehicle swings out to the left in a skid, you should correct the problem by turning the steering fully to the left. Some people express it by saying, steer in the direction of a rear-wheel skid. Others say, counter steer to straighten out the vehicle. If you have never experienced a skid, you might consider taking a course designed to give you the skill. Otherwise, practice in an unoccupied snow-covered parking lot.
Abbreviation for oxygenated fuels program reformulated gasoline
Abbreviation for options or Optional equipment.
Optical check
  1. A cursory visual inspection.
  2. An examination with optical instruments
To set at the best possible value
Optional equipment
Any equipment or feature of a new vehicle which is not included in the basic price and is provided only if the purchaser requests it. The opposite is Standard equipment


Extra features which may be purchased or may be included in the normally standard list of features and appointments of a vehicle.
Orange Circle
Orange peel
A rough paint surface, resembling the skin of an orange caused by the paint spray failing to flow together.
Orbital sander
A flat, cushioned plate covered with abrasive paper, rotated with an elliptical motion by an electric motor and used for fine sanding work like feather edging.

Abbreviation for Oxidation Reduction Converter
Order Selector
Also known as an order picker, an order selector is a specialized lift truck that allows a person to ride on it with the pallet in order to pick from various locations and levels.
Ore-bulk-oil carrier
A multipurpose ship that can carry ore, dry bulk goods, and oil. Also called OBO ship
Ore carrier
A large ship designed for the transportation of ore.
  1. Something of chemical compounds that are based on carbon chains or rings and containing hydrogen with or without oxygen, nitrogen, or other elements. The opposite is Inorganic
  2. Pertaining to or derived from living organisms.
Organic Carbon
Organic Compound
Organic content
The share of a substance that is of animal or plant origin.
Organic Fraction
Organic friction material
A friction material having organic binders, substantially formulated with non-metallic fibers.
Organic Gases
Organic linings
Brake lining material using asbestos as its main ingredient
Organic Matter
Organization for Economic Co-operation and Development

  1. An international organization helping governments tackle the economic, social and governance challenges of a globalized economy. Its membership comprises about 30 member countries. With active relationships with some 70 other countries, NGOs and civil society, it has a global reach. For details about the organization, visit
  2. An organization whose purpose is to provide its 29 Member countries with a forum in which governments can compare their experiences, discuss the problems they share and seek solutions which can then be applied within their own national contexts. Each member country is committed to the principles of the market economy and pluralistic democracy.
Organization of the Petroleum Exporting Countries
(OPEC) An intergovernmental organization whose stated objective is to coordinate and unify petroleum policies among member countries. It was created at the Baghdad Conference on September 10-14, 1960, by Iran, Iraq, Kuwait, Saudi Arabia and Venezuela. The five founding members were later joined by nine other members: Qatar (1961); Indonesia (1962); Libya (1962); United Arab Emirates (1967); Algeria (1969); Nigeria (1971); Ecuador (1973-1992, 2007); Gabon (1975-1994) and Angola (2007).
The tendency of plastic molecules if stretched, to align themselves in the direction of the stress. Molecular orientation leads to Anisotropy of mechanical properties (i.e., having different mechanical properties in different directions). This can be used to advantage in the production of fibers and film or may be the undesirable result of a molding process
  1. Opening through which gases flow. It is usually the final opening, or any opening controlled by a valve.
  2. Accurate size opening for controlling fluid flow.
  3. The opening in an orifice cap, orifice spud or other device whereby the flow of gas is limited and through which the gas is discharged.
Orifice cap
A movable fitting, having an orifice which permits adjustment of the flow of gas by changing its position with respect to a fixed needle or other device. Also called orifice hood
Orifice hood
A movable fitting, having an orifice which permits adjustment of the flow of gas by changing its position with respect to a fixed needle or other device. Also called orifice cap
Orifice spark advance control
(OSAC) a device used by Chrysler to apply vacuum advance over a period of time. By limiting the timing advance rate, NOx is reduced
Orifice spud
A removable plug or cap containing an orifice which permits adjustment of the flow of gas either by substitution of a spud with a different size orifice or by motion of a needle with respect to it.
Orifice tube
Metering device consisting of a restricting tube with inlet and outlet screens.

Orifice valve
Abbreviation for original, as in orig. owner.
Original condition
An older vehicle that has all of its original paint and equipment and has not been restored or modified.
Original equipment
These are the items on a vehicle which came from the manufacturer. It does not include accessories produced by Aftermarket companies (sometimes called jobber). Generally original equipment parts are the best for the vehicle. Although it must be admitted that some aftermarket products are better quality and may be less money; however the opposite is also true.
Original equipment manufacturer

  1. A generic term that refers to an automobile company or supplier which manufactures the parts used in the original assembly a vehicle.
  2. Manufacturers of equipment (such as engines, vehicles, etc.) that provide the original product design and materials for its assembly and manufacture. OEMs are directly responsible for manufacturing and modifying the products, making them commercially available, and providing the warranty.
  3. A company that provides the original design and materials for manufacture and engages in the assembly of vehicles. The OEM is directly responsible for manufacturing, marketing, and providing warranties for the finished product.
Original equipment manufacturer vehicle
A vehicle produced and marketed by an original equipment manufacturer (OEM), including gasoline and diesel vehicles as well as alternative-fuel vehicles. A vehicle manufactured by an OEM but converted to an alternative-fuel vehicle before its initial delivery to an end-user (for example, through a contract between a conversion company and the OEM) is considered to be an OEM vehicle as long as that vehicle is still covered under the OEM’s warranty.
Original finish
The paint applied to vehicle when it is built by the manufacturer.
O ring

An o-ring is a doughnut shaped (annular) rubber or plastic ring which is placed in a groove and compressed to seal fluid or gas from passing a particular point.
O-ring chain
O-ring chain
O-ring chains
A drive chain (usually used on motorcycles) which has small neoprene o-rings within the exposed rollers to encircle the pins. The o-rings help to prevent dust from getting in and thus the chain lasts much longer.
Orphan bikes
Rare bikes that are no longer in production
Abbreviation for Onboard Refueling Vapor Recovery.

Abbreviation for Offside
Abbreviation for Oxygen Sensor
Abbreviation for Orifice Spark advance control
Abbreviation for Over, Short and Damage which refers to the a load of product which arrives in a defective condition, or whose quantity does not match the bill of lading (cases over or short).
Abbreviation for Output State Check (Ford)
A vehicle brand of which the 1948-56 MT-4 models are milestone cars.
To swing back and forth like a pendulum.
Oscillating action
A swinging action such as that in the pendulum of a clock.
Oscillating pick-up ignition system
(OPUS) An ignition system where the contact breaker and cam are replaced by a timing rotor, a pick-up module, and an amplifier module
A swinging action such as that in the pendulum of a clock.

  1. A testing unit which projects visual reproduction of the ignition system spark action onto screen of cathode-ray tube.
  2. Fluorescent-coated tube which visually shows an electrical wave.
Abbreviation for Otomotiv Sanayii Dernegi (i.e., Automotive Manufacturers Association) (Turkey)
Abbreviation for Occupational Safety and Health Administration. A division of the US Department of Labor that oversees and regulates matters affecting safety in the workplace.
Abbreviation for Output State Monitor
Abbreviation for Output Speed Shaft
  1. Abbreviation for Outdoor temperature gauge
  2. Abbreviation for Outside temperature gauge
Abbreviation for Overhead Travel Information System
  1. Abbreviation for Off-road tire
  2. Abbreviation for over-the-road
Otto cycle
Four-stroke cycle consisting of the intake, compression, firing, and exhaust strokes, in honor of the German engineer Dr. Nikolaus Otto (1832- 1891) who first patented the design in 1876.

Abbreviation for Oil thermal vacuum switch
Ounce inches
An expression of the force exerted by a heavy spot (or counterbalance weight) on a tire. Multiply the weight times its distance from the axle center, i.e., 3 oz. x 7′ = 21 ounce inches.
Space left in a product container to allow for expansion during the temperature changes it may undergo during shipment and application. Measurement of space that is NOT occupied in a drum.
  1. Something away from the center of a vehicle.
  2. Away from the centerline and towards the side. Outside the hull
Outboard contre pente
Safety contour for tubeless passenger car wheel rims, featuring a Contre pente on the outer bead seat
Outboard flat hump
A safety contour for tubeless passenger car rims, featuring a flattened hump on the outer bead seat
Outboard flat pente
A safety contour for tubeless passenger car rims, featuring a flattened contre pente on the outer bead seat
Outboard motor
A boat motor which is attached to the rear of a small boat
Outboard round hump
A safety contour for tubeless passenger car rims, featuring a round hump on the outer bead seat
Outdoor temperature gauge
(otg) A gauge which indicates the ambient air temperature outside the vehicle
Outer bulb
Outer cap nut
A securing device on a dual mounted disc wheel type where it threads directly on the Inner cap nut and holds the outer wheel in place against the hub.
Outer construction
The basic skin of a vehicle’s body, i.e., those parts which are visible from the outside of the vehicle. In contrast to the Inner construction
Outer dead center
Outer diameter
(OD) The external diameter of a cylinder or tube
Outer electrode
  1. The outer terminal.
  2. The ground electrode
Outer envelope
The bulb of a gas discharge lamp which protects and supports the arc tube; either filled with gas or evacuated to avoid oxidation of the arc tube
Outer headlight
On a headlight system where there are four lights (two on each side), the outer headlights (low beam) are at the extreme outside (i.e., the furthest away from the center of the car).

Outer lane
The lane nearest the center of the road. In those countries that drive on the right side, it is the lane to the farthest left without crossing over to the on-coming lane. In those countries where they drive on the left side, it is the farthest to the right without crossing over to the on-coming lane.
Outer race
Bearing RaceBearing Race

The outer track or ring that provides a contact surface for the balls or rollers in a bearing.

Outer sill
Outer sill
A ledge below the doors visible from the outside; often referred to as the sill, whereas the inner sill is actually the side member
Outer terminal
The electrode on the inside of the distributor cap, one outer terminal being assigned to each spark plug; the distributor rotor distributes the firing voltage from the central electrode to the outer terminals. The opposite is Center electrode
Outer tower
A socket on the distributor cap corresponding to the outer terminal, one per cylinder, to connect the spark plug leads
Outer Wheel Path Paving
This treatment is used for roads where the outer wheel path of the road is excessively out of shape, usually marked by excessive cracking and wheel ruts. It is also often preceded by box-out repairs. The paving is done continuously, about 4-5′ wide on the outside wheel path of both lanes. This work may take several days, depending on the length of the road section. This work is often followed by a surface treatment.
Outer wrap
Something that surrounds the converter shell of a catalytic converter and serves as a retainer and provides mechanical protection for the insulation
A fabric by Outlast Technologies that absorbs, stores and releases body heat, making this thermal layer critical technical equipment for all your cold weather adventures.
  1. Synonymous with vehicle dealership.
  2. The exhaust port of 4-stroke engine.
  3. The rear opening of a catalytic converter or muffler.
  4. The last pipe of an exhaust system (i.e., the tailpipe).
Outlet pipe
A pump discharge pipe
Outlet side
That side of the pump or pumping system on which the liquid pumped leaves the pump or system. The opposite is suction side
Outlet valve
To mold plastic material around something. Compare Insert
Out-Of-Pocket Cost
Out of round
  1. Something that is not completely circular. For instance a wire wheel may be true in that it does not wobble from side to side, but it may have a flat spot.
  2. A condition where engine cylinder bore has greater wear at one diameter than another
  3. The condition of brake drum when it has become distorted and is no longer perfectly round. In many cases an out of round brake drum can be salvaged by resurfacing on a brake lathe
Out of true
Something inaccurately made or incorrectly adjusted, e.g., of a wheel with side-to-side deviation or wobble
Out of tune
An engine which is not running ideally and needs a Tune up
Output driver
A transistor in the output control area of the computer that is used to turn various actuators on and off
Output shaft
The shaft delivering power from within a mechanism. The shaft leaving the transmission, attached to the Propeller shaft or driveshaft, is the transmission output shaft.

Output speed
The speed of the transmission output shaft which is transmitted to the driven wheels via the final drive; as the final drive provides a constant gear ratio, output speed is proportional to vehicle road speed
Output voltage
The fundamental rms (root mean square) voltage between the output terminals.
  1. A device with retractable mechanical legs used to stabilize equipment such as cranes, ditch diggers, etc., while working.
  2. A short angle or box section member that runs across part of the car. On cars with separate frames, outriggers are used to link the main chassis or the longitudinal members with the sill or running board area. An outrigger is far shorter and often of a smaller section than a crossmember
  3. Leg-like extensions used on the front or rear of machinery to improve stability.
  4. Structural load-carrying members attached to and extending from the main frame of a trailer.
  1. A device with retractable mechanical legs used to stabilize equipment such as cranes, ditch diggers, etc., while working.
  2. A short angle or box section member that runs across part of the car. On cars with separate frames, outriggers are used to link the main chassis or the longitudinal members with the sill or running board area. An outrigger is far shorter and often of a smaller section than a crossmember
  3. Leg-like extensions used on the front or rear of machinery to improve stability.
  4. Structural load-carrying members attached to and extending from the main frame of a trailer.
outside caliper
Outside caliper
Outside caliper
A machinists’ caliper used to check outside dimensions.

Outside corner weld
Fusing two pieces of metal together, with the fusion taking place on the underpart of the seam.
Outside diameter
The external diameter of a cylinder or tube
Outside spring caliper
An Outside caliper with a spring for accurate setting
Outside temperature gauge
(otg) A gauge which indicates the ambient air temperature outside the vehicle
To shape the road surface to cause drainage to flow toward the outside shoulder.
Oval Binding Head Screw
Obsolete term for a truss head screw.
Ovalhead machine screw
Ovalhead machine screwOvalhead machine screw

A machine screw that fits a countersunk hole, but upperside is a dome shape.

Oval head screw
A fastener with a rounded top surface and a conical bearing surface with an included angle usually of 82 degrees.
Oval piston
A special piston developed by Honda, able to accommodate eight valves and two spark plugs
Oval Point
A rounded end which is used, particularly for set and adjusting screws, to apply pressure without cutting action.
Oval point socket set screw
A headless socket set screw threaded the entire length. It has a hexagonal drive at one end and an oval shaped point at the other end.
Colloquial term for tires. Wide Ovals are wide tread tires.
Oval track
A race course which is shaped like an oval rather than a circle. Sometimes used to describe any race track, other than a road race.
Abbreviation for Outer Vent Control Valve
Oven head
Old term for truss head.
Oven Head Screw
Obsolete term for truss head screw.
Overall gear ratio
The ratio of engine revolutions to road wheel revolutions, producing road speed as a ratio of engine speed (sometimes expressed as mph per 1000 rpm)
Overall length
The extreme length of a ship measured from the foremost point of the stem to the aftermost part of the stern
Overall ratio
Overall repainting
A type of paint job that involves the entire vehicle
Overall rim diameter
A measurement from the top of the flange to opposite top of the flange 180° away.
Overaxle pipe
To drill out the cylinder and put in larger pistons to increase the capacity or clean up damaged cylinder walls
The situation where maximum global production of automobiles exceeds the total global demand for automobiles.
  1. Refers to the condition that occurs when too much refrigerant or oil is in the system
  2. To keep a storage battery on the charger beyond recommended limits or at a higher voltage than recommended.
Vulcanizing a tire longer than necessary. It can result in the deterioration of certain physical properties.
  1. A unit with a Planetary gearset which turns the driveshaft faster than the transmission Output shaft.
  2. An additional Gearbox which is mounted in the Driveline. Normally the Final drive ratio is 11; but the overdrive makes it less (e.g., 0.871). The overdrive can reduce gas consumption at sustained high-speed driving, engine noise, and engine wear. Also called overdrive transmission.
  3. Gearing in which less than one revolution of a transmission’s input shaft causes one turn of the output shaft. The purpose of overdrive is to reduce engine rpm in high gear for better fuel economy. Example A transmission with an overdrive top gear has a ratio of 0.70 to one. Turning the input shaft 0.7 revolutions causes 1.0 revolution of the output shaft.
Overdrive transmission
A transmission with a High gear which acts as an Overdrive.
To spew out tread compound at the mold parting line or at the edge of the matrix skirt. This excess material should be trimmed or buffed off the finished product.
Overflow hose
A tube located in the radiator fill hole that allows excess liquid to escape from the cooling system under conditions of extreme heat, pressure, or overfilling.

Overflow pipe
A tube located in the radiator fill hole that allows excess liquid to escape from the cooling system under conditions of extreme heat, pressure, or overfilling.

The distance between the outermost front or rear point of a vehicle and the wheel centers of the respective axle.

Overhead cam (OHC)
Overhead cam engine
Overhead camshaft
(OHC) The camshaft that activates the valves is mounted above the head and driven by a long Timing chain or Cam chain. In contrast, a pushrod engine has the camshaft below the cylinders so that thin rods (pushrods) are moved by the camshaft and activate the valves. An engine with an overhead cam means that the distance between the cam and the valves is much shorter, so the valves respond quicker and valve adjustment can be more accurate. Also this system allows for higher Engine speed because of fewer moving Valvetrain parts. A system with only one cam is called Single Overhead Cam (SOHC). In some instances there are two camshafts above the heads (one for the intake valves and the other for the exhaust) and called Double overhead cam (DOHC).

Overhead position
A weld made on the underside of the joint with the face of the weld in a horizontal plane.
Overhead valve engine
(OHV) An engine with its valves located in the head. A four-stroke engine with the intake and exhaust poppet valves located in the cylinder head and not at the side of the cylinder as in a side-valve engine. The valve stems are either at an angle or parallel and the valve discs face the piston, valve actuation pushrod and swing arm.
Overhead valves
(OHV) Valves located in the head. A four-stroke engine with the intake and exhaust poppet valves located in the cylinder head and not at the side of the cylinder as in a side-valve engine. The valve stems are either at an angle or parallel and the valve discs face the piston, valve actuation pushrod and swing arm.

To make or become too hot. Engine overheating could be caused by a fault in the cooling system caused by a leak, blockage, slipping or broken fan belt; lack of engine oil; or an over-lean mixture. Brake overheating can be caused by prolonged use (e.g., when going downhill) leading to brake fade, binding brake shoes, or seized disc pads or pistons
Overinflated tire
A tire which has too much air in it, causing premature wear in the tread center. The opposite is Underinflated tire
Over inflation
Excessive tire pressure in relation to the tire size and load carried. It will generally result in wear at the center of the tire tread rather than the outer sides.
  1. The part of the spray band that covers the previous application of paint. A 50% overlap on each stroke is generally recommended.
  2. Extension of the weld face metal beyond the toe of the weld.
  3. The number of degrees of crankshaft rotation where the both the intake and exhaust valves are open at the same time. This situation will occur only at the end of the exhaust stroke and the beginning of the following Intake stroke.
  1. The upper layer of a plain bearing insert. If the overlay is worn, the bearing material beneath it will still allow for a certain emergency operation of the component supported in the plain bearing
  2. A new layer of pavement placed on a road’s surface. During the process, hot oil is sprayed on the road, then chips are applied on top of it to seal the road. Generally applied to full width of existing roadway surface, to provide smoother riding surface.
Overlay sprocket
A sprocket with a large center hole and is bolted to an existing sprocket to change the gear ratio.
Overlay paint
A special type of custom paint where a design on the painted surface is embedded below a coat of translucent paint, giving the impression that two paints are applied to the car. Compare Candy paint
  1. Carrying more weight on a tire than its listed maximum carrying capacity or carrying excessive loads on a tire in relation to its inflation (esp. if underinflated).
  2. Load greater than that for which system or mechanism was intended.
Overload protector
Device, either temperature, pressure, or current operated, which will stop operation of unit if dangerous conditions arise.
Overload spring
A chassis spring which acts only under heavy load and prevents bottoming
To run an engine above the maximum recommended rpm. To exceed the redline on the tachometer
Override button
A short, vertical attachment to the bumper, to prevent interlocking with other bumpers
  1. A vehicle traveling with no throttle and the engine acting as a brake is said to be on the overrun or overrunning.
  2. The action of a trailer when it travels faster than the towing vehicle
Overrun brakes
Trailer brakes activated by the tendency of the trailer to overtake (i.e., overrun) the towing vehicle when the vehicle brakes or slows down.
Overrun control valve
A valve in a crossover pipe between the compressor suction and discharge sides of some turbocharger systems. When the manifold pressure drops, as during deceleration, the overrun control valve opens and allows compressed air to circulate through the compressor again; this maintains turbo speed on the overrun, minimizing turbo lag when the throttle is re-opened; not to be confused with a safety-relief valve in the compressor discharge line or with a wastegate valve
Overrun cut-off/shut-off
Overrunning clutch
  1. A clutch mechanism that will drive in one direction only. If driving torque is removed or reversed, the clutch slips.
  2. A part of a starter motor designed to avoid armature damage caused by severe overrevving.
  3. A device in an automatic transmission that disengages the engine on overrun
Overrunning clutch starter
Overrunning clutch starter drive
A Starter drive that is mechanically engaged. When the engine starts, the Overrunning clutch operates until the drive is mechanically disengaged.

Overrunning coupling
Installing a tire larger than needed to carry the load. A common (though not always beneficial) practice on passenger vehicles to increase one size when replacing OEM tires.
Oversize brake shoes
Brake shoes with thicker linings designed for use in drums that have been machined oversize.
Oversize piston
A piston with a diameter slightly larger than that of the standard piston, used in order to allow for a honing of the cylinder walls
Oversize valve guide
A valve guide with a slightly larger outside diameter than the standard valve guide, used to repair worn valve guides after their bores have been reamed
The fine mist of paint on areas where it is not wanted (glass, moldings, other painted surfaces, etc). The distinguishing mark of a vehicle that has been painted or had body work done. Compare Spray mist
An engine where the cylinder Bore diameter is greater than the length of the stroke.
Over square engine
An engine in which the Bore diameter is larger than the length of the stroke.
The tendency for a vehicle, when negotiating a corner, to turn more sharply than the driver intends. The rear end of the vehicle wants to swing toward the outside of a turn. It is generally a sign that the suspension roll resistance is too hard in the rear or too soft in the front. A rear-engine vehicle has a natural tendency to want to swap ends, or oversteer, unless its suspension is adjusted to counteract it. A handling condition in which the Slip angles of the rear tires are greater than the slip angles of the front tires. An oversteering car is sometimes said to be loose, because its tail tends to swing wide.

To pass another vehicle going in the same direction
The action of your passing a vehicle which is going in the same direction you are.
A trucking expression to indicate travel from one city to another, as distinct from travel in and around the vehicle’s base.
To add too much thinner to paint
Includes pay received for the number of hours worked in excess of the standard workday or workweek.
The application of too much power to the wheels so that instead of propelling the vehicle, the wheels spin. When a vehicle is stuck in snow, there is a tendency to apply too much power in the belief that the vehicle needs as much force to get out of the problem, but the wheels just spin and create an icy patch that is even harder to get out of. An even amount of power is needed to slowly move the wheels so that they maintain their grip.
Over-travel spring
A special assembly on some cable-actuated starwheel automatic adjusters that prevents over-adjustment or damage.
A voltage above the normal rated voltage or the maximum operating voltage of a device.
Overvoltage relay
A relay used to protect the electronic control units
Over your shoulder
Trucker slang for behind the driver as in ‘How’s it look over your shoulder?’
Someone who actually owns something, i.e., has the title of property.

Owner’s handbook
A booklet provided with a new car which briefly describes the position and operation of the various instruments and switches, as well as technical specifications and some maintenance information. Also called Owner’s manual
Owner’s manual
Every new vehicle is supplied with a handbook which gives the basic instructions for operating the controls. It includes a maintenance schedule and Specifications such as the type and quantity of fluids. For instruction on repair work, you will need a Service manual which may be ordered from the dealership which sold you your vehicle.
Owner Operator
  1. A trucker who owns and operates his own truck(s)
  2. A for-hire carrier who both owns and drives a vehicle and serves as the operating authority.
Oxalic acid
An acid used as an electrolyte for anodizing
  1. One of the processes by which Enamel paint cures, by combining oxygen in the air with the paint film. This process dries and continues to harden enamel for several weeks. Oxidation also results in Chalking in older paint.
  2. A chemical reaction which increases the oxygen content of a compound or in which a compound or radical loses electrons, i.e., in which the positive valence is increased. Compare Reduction
  3. A form of corrosion caused by reacting a substance with oxygen.Rust (iron oxide) is a typical example.
Oxidation Burner
Oxidation catalyst
(OC) type of bead material in catalytic converter which aids in oxidation of CO and HC

A chemical compound of oxygen with another element.

Oxide film
Oxide Fuel Cell
Oxide layer
Oxide skin
Oxides of nitrogen
(NOx) Regulated air pollutants, primarily NO and NO2 but including other substances in minute concentrations. Under the high pressure and temperature conditions in an engine, nitrogen and oxygen atoms in the air react to form various NOx. Like hydrocarbons, NOx are precursors to the formation of smog. They also contribute to the formation of acid rain.

Oxide system
Action where surface of metal is combined with oxygen in the air to produce rust, Scale, etc.
A compound which gives up oxygen easily, removes hydrogen from another compound, or attracts electrons.

The combining of oxygen with any other substance. For example, a metal is oxidized when the metal is burned, i.e., oxygen is combined with all the metal or parts of it.
Oxidizing agent
  1. A compound which gives up oxygen easily, removes hydrogen from another compound, or attracts electrons
  2. Any substance such as oxygen and chlorine, that can accept electrons. When oxygen or chlorine is added to wastewater, organic substances are oxidized. These oxidized organic substances are more stable and less likely to give off odors or to contain disease bacteria.
Oxidizing catalyst
A catalyst which decreases CO and HC levels using excess air. Compare Reducing catalyst
Oxidizing converter
A converter with a conventional oxidation catalyst that needs a secondary air supply to convert hydrocarbons and carbon monoxide to carbon dioxide and water; does not control NOx. Compare Single-bed oxidizing converter

Oxidizing flame
Flame produced by an excess of oxygen in the torch mixture, leaving some free oxygen which tends to burn the molten metal.
Abbreviation for Oxygen sensor
Oxyacetylene welding
A gas formed of the element oxygen. When it very actively supports combustion it is called burning; when it slowly combines with a substance it is called oxidation.
Oxygen acetylene cutting
Cutting metal using the oxygen jet which is incorporated with an oxygen-acetylene, preheating flame or flames.
Oxygen-acetylene welding
A method of welding, using as a fuel a combination of the two gases – oxygen and acetylene.
  1. To treat, combine, or infuse with oxygen.
  2. A term used in the petroleum industry to denote fuel additives containing hydrogen, carbon and oxygen in their molecular structure. Includes ethers such as MTBE and ETBE and alcohols such as ethanol and methanol.
Oxygenated Fuel
Any fuel substance containing oxygen, such as ethanol, methanol, or Biodiesel. Oxygenated fuel tends to give a more complete combustion of its carbon into CO2, thereby reducing emissions of hydrocarbons and carbon monoxide. Oxygenated fuels may result in increased nitrogen oxides emissions.
Oxygenated gasoline
  1. Any fuel with a mixture of ethyl or methyl alcohol. The addition of oxygen causes a slightly leaner fuel-air mixture which is especially beneficial with older vehicles.
  2. Finished motor gasoline, other than reformulated gasoline, having an oxygen content of 2.7 percent or higher by weight and required by the U.S. EPA to be sold in areas designated by the EPA as CO nonattainment areas. Oxygenated gasoline excludes oxygenated fuels program reformulated gasoline (OPRG) and reformulated gasoline blendstock for oxygenate blending (RBOB).
Oxygenated gasolines
Oxygenate Plants
An oxygen-enriched fuel or anti-knock additive. Substances which, when added to gasoline, increase the amount of oxygen in that gasoline blend. ethanol, MTBE, ETBE, and methanol are common oxygenates.
Oxygen corrosion
An electrochemical corrosion caused by neutral or alkaline electrolytes in which, during the cathodic reaction, oxygen is reduced to hydroxide
Oxygen cylinder
A specially built container manufactured according to I.C.C. Standards and used to store and ship certain qualities of oxygen.
Oxygen-hydrogen flame
The chemical combining of oxygen with the fuel gas hydrogen.
Oxygen-LP gas flame
Chemical combining of oxygen with the fuel gas LP (liquefied petroleum).
Oxygen regulator
An automatic valve used to reduce cylinder pressures to torch pressures and to keep the pressures constant. They are never to be used as acetylene regulators.
Oxygen sensor
Oxygen sensorOxygen sensor

(OXS) A pollution control device which measures the amount of oxygen in the exhaust stream and sends that information the ECM. It controls the fuel-air mixture entering the engine. Also called a lambda sensor, exhaust oxygen sensor, or an O2 sensor

Oxygen sensor system thermo-switch
A detection device that monitors the fuel injection system and is usually located in a coolant hose to provide a coolant temperature signal to the ECM
Oxygen Storage Capacity
(OSC) A capacity of the catalyst washcoat to store oxygen at lean and to release it at rich condition. Typically provided by cerium oxide (ceria), which oscillates between an oxidized and reduced state, depending on the exhaust gas chemistry. The OSC is an important component of three-way catalysts, used to extend the catalyst window.
Oxygen-to-carbon ratio
The ratio of the number of oxygen atoms to the number of carbon atoms in the fuel (e.g., methanol would have a ratio of 1, ethanol would have 0.5).
Oxyhydrogen gas
A highly explosive mixture of oxygen and hydrogen, generated during charging of lead-acid batteries. Compare Gassing
The application of ozone to water, wastewater, or air, generally for the purposes of disinfection or odor control.

  1. An oxygen molecule with three oxygen atoms. The stratosphere ozone layer, which is a concentration of ozone molecules located at 10 to 50 kilometres above sea level, is in a state of dynamic equilibrium. Oxygen molecules absorb ultraviolet light to form ozone which, in turn, decomposes back to oxygen. These processes absorb most of the ultraviolet light from the sun, shielding life from the harmful effects of UV radiation. Ozone is normally present at ground level in low concentrations. In cities where high level of air pollutants is present, the action of the sun’s ultraviolet light can, through a complex series of reactions, produces harmful concentrations of the ground level ozone. The resulting air pollution is known as photochemical smog.
  2. A faintly blue form of oxygen produced by the silent discharge of electricity into the air. Ozone is very harmful to tires.
Ozone checking
Cracks or hard spots usually found on the sidewalls of tires. Caused by the action of the ozone in the air on the rubber. This condition is normal, but could be dangerous on tires that are more than 65,000 km (40,000 miles) old or have been exposed to the ozone created by electrical machinery.
Ozone compound
Rubber compounded with certain chemicals to retard ozone damage. Properly this should be called anti-ozone compound.
Ozone precursors
Chemical compounds, such as carbon monoxide, Methane, nonmethane hydrocarbons, and nitrogen oxides, which in the presence of solar radiation react with other chemical compounds to form ozone.