Glossary of Automotive Terms – V

Letter V – Dictionary of Automotive Terms

  1. A letter rating for tires to indicate that they are theoretically rated for speeds up to 210 kph (130 mph), as in P220VR15. The next higher rating is W and the one lower rating is H.
  2. A letter indicating a valve configuration as in 16v meaning a 16 valve engine.
  3. A letter indicating the configuration of the cylinders in an engine as in V-8
  4. Abbreviation for Volts












Value analysis.
Abbreviation for Vacuum
Vac servo
  1. An enclosed area in which the air pressure is below that of the surrounding atmospheric pressure.
  2. Technically, a complete absence of pressure (0 psi), although the term is commonly used to describe any pressure less than atmospheric.
Vacuum activators
Dampers and control valves used in automotive air conditioning system controlled by the vacuum created by engine intake manifold vacuum.
Vacuum advance
A mechanism on the side of the distributor that automatically varies the instant at which the spark occurs as a function of intake manifold vacuum. Vacuum advance provides the additional advance that is needed when the engine is operating at part throttle. At part throttle less air-fuel mixture gets into the cylinders and the mixture takes longer to burn after it is ignited. Because the mixture burns more slowly, the piston will be past Top dead center and moving down before the mixture has a chance to burn and produce high power. As a result much of the power in the fuel will be lost. The vacuum advance mechanism consists of a flexible spring-loaded diaphragm connected by a linkage to the Breaker plate on which the points are mounted. The sealed side of the diaphragm is connected by a tube to the carburetor. The Throttle valve is below the vacuum passage in the carburetor Air horn so there is no vacuum advance when the engine is idling because the throttle is closed. However, when the throttle is partly open, intake manifold vacuum pulls the diaphragm in and this causes the Breaker plate to rotate a few degrees and advance the timing. With wide-open throttle there is very little vacuum in the intake manifold so there will be no vacuum advance. In most instances the vacuum advance is disconnected before checking the timing and Point gap.

Vacuum advance mechanism
Vacuum advance unit
Vacuum assisted brake
Vacuum assisted brakes
Vacuum assist unit
An actuating mechanism that uses vacuum on one side of a diaphragm as a source of power.
Vacuum booster
  1. A small diaphragm Vacuum pump, generally in combination with the fuel pump, that is used to bolster engine vacuum during acceleration so that the vacuum operated devices will continue to operate.
  2. A power brake actuating mechanism that uses vacuum on one side of a diaphragm as a power source.
Vacuum brake booster
A device directly connected to the master cylinder and mounted on the engine side of the bulkhead, which uses engine manifold vacuum to produce additional braking force
Vacuum brake supply line
The conduit for transmitting supply vacuum from a vacuum source to the vacuum reservoirs.
Vacuum brake system
A brake system that uses engine vacuum to operate and control.
Vacuum Bypass System
Vacuum capsule
A pneumatic actuator that converts air pressure differences into a regulating short-stroke movement; the circular, flat capsule has a spring-loaded diaphragm with a lever attached
Vacuum chamber
A pneumatic actuator that converts air pressure differences into a regulating short-stroke movement; the circular, flat capsule has a spring-loaded diaphragm with a lever attached
Vacuum check valve
(VCK-V) a one-way valve used to retain a vacuum signal in a line after the vacuum source is gone
Vacuum control
A load-dependant mechanical ignition timing, controlled by the inlet manifold vacuum
Vacuum control switch
A switch that monitors the vacuum signal enabling the ECU to recognize open or closed throttle (idle) operation
Vacuum control system
Intake manifold vacuum is used to operate dampers and controls in some automobile systems.
Vacuum control unit
An assembly for load-dependent ignition timing controlled by the intake manifold vacuum, consisting of a vacuum capsule with a spring-loaded diaphragm linked to the breaker plate
Vacuum control valve
(VCV) a ported vacuum switch, controls vacuum to other emission devices during engine warm up
Vacuum delay valve
(VDV) a valve used by GM to bleed ported vacuum to the vacuum advance unit through a small orifice and control vacuum advance rate. Used to retard or delay the application of a vacuum signal. Also called Delay valve
Vacuum differential valve
(VDV) a device used in a Thermactor system with a catalyst that sense intake manifold vacuum and triggers the bypass valve to dump injection air to the atmosphere during deceleration
Vacuum distillation
Distillation under reduced pressure (less the atmospheric) which lowers the boiling temperature of the liquid being distilled. This technique with its relatively low temperatures prevents cracking or decomposition of the charge stock.
Vacuum-electric Switch

Vacuum-electric SwitchVacuum-electric Switch

A component which gives gross reading of vacuum in the intake manifold by using a diaphragm to operate a simple on-off electrical switch.

Vacuum filter
A filter which removes electrical noise from the vacuum signal sent from the vacuum sensor to the ECU
Vacuum gage
Vacuum gauge
A gauge used to determine the amount of vacuum existing in a chamber.
Vacuum hose
A pipe which connects the intake manifold to the vacuum brake booster
Vacuum hublock
Vacuum hydraulic power unit
A unit consisting of a vacuum brake cylinder or chamber, hydraulic cylinder(s) and control valve, in which driver effort is combined with force from the cylinder piston or chamber diaphragm to displace fluid under pressure for actuation of the brake(s).
Vacuum ignition-timing control
Vacuum leak
A loss of vacuum from a leaking hose or defective gasket
Vacuum modulated EGR
An exhaust gas recirculation in which the amount of exhaust gas admitted to the intake manifold depends on a vacuum signal controlled by throttle position. When the throttle is closed, at idle or during deceleration, there is no vacuum signal to the EGR valve; as the throttle is opened, a vacuum signal is supplied causing the EGR valve to open
Vacuum modulator
A small unit attached to the automatic transmission. If the vehicle tends to stay in Low gear, shifts with difficulty or produces whitish smoke, has an automatic transmission, and is constantly low in Transmission fluid, try replacing the vacuum modulator before undertaking major repairs. Most vacuum modulators simply screw into place.


Vacuum motor
A vacuum-actuated device used to operate doors and valves.

Vacuum operated exhaust heat control valve
(VHC) a vacuum operated heat riser valve used by Ford to cause the exhaust to flow through the intake crossover passage for preheating of the air-fuel mixture
Vacuum over hydraulic brake system
A hydraulic-type brake system actuated by a vacuum-powered master cylinder.
Vacuum-powered master cylinder
A brake master cylinder actuated by a vacuum cylinder or chamber.
Vacuum power motor
A device for use in opening doors in heating and air conditioning systems
Vacuum power unit
A device for use in opening valves and doors in heating and air conditioning systems using vacuum as a source of power.
Vacuum pressure
Any pressure less than that exerted by the atmosphere.
Vacuum pump
  1. A diaphragm type of pump used to produce a vacuum.
  2. A special high efficiency device used for creating high vacuums for testing or drying purposes.
  3. A mechanical device used to evacuate an air conditioning system to rid it of moisture, air, and contaminants.
  4. A device which creates a vacuum to actuate the brakes.
Vacuum reducer valve
(VRV) A valve used by GM to limit the amount of vacuum governing the ignition advance mechanism of the distributor; on some ignition systems, a VRV is used to reduce intake manifold vacuum when the coolant temperature is above 104°C, in order to prevent or reduce detonation
Vacuum regulator valve three and four-port
(VRV) this type of vacuum regulator valve is used to control the vacuum advance to the distributor
Vacuum regulator valve two-port
(VRV) this vacuum regulator provides a constant output signal when the input level is greater than a preset level. At a lower input vacuum, the output equals the input
Vacuum relief valve
A valve which automatically opens and closes a vent for relieving a vacuum within the a system, depending on whether the vacuum is above or below a predetermined value.
Vacuum reservoir
(VRESER) stores excess vacuum to prevent rapid fluctuations and sudden drops in a vacuum signal, such as during acceleration
Vacuum restrictor
(VREST) controls the flow rate and/or timing in actions to the different emission control components
Vacuum retard
A vacuum control unit for retarding the spark
Vacuum retard delay valve
(VRDV) delays a decrease in vacuum at the distributor vacuum advance unit when the source vacuum decreases. Used to delay release of vacuum from a diaphragm — a momentary vacuum trap
Vacuum retard unit
A vacuum control unit for retarding the spark
Vacuum runout point
The point reached when a vacuum brake power piston has built up all the braking force it is capable of with the vacuum available.

Vacuum sealing apparatus
A component in continuous zinc vapor deposition lines through which steel strips enter the deposition chamber and which prevents a build-up of pressure within the chamber
Vacuum sensor
A detection device which monitors changes in manifold pressure in comparison to barometric pressure; such changes indicate the need for an adjustment in air/fuel mixture and electronic spark timing to maintain efficient engine operation. Also called Manifold pressure sensor, Pressure differential sensor, or Manifold vacuum sensor

Vacuum servo
A flexible diaphragm with a linkage attached to it installed in a sealed housing. When vacuum is applied to one side of the diaphragm, atmospheric pressure on the other side moves the diaphragm and linkage to perform work.

Vacuum solenoid
On some engines, a vacuum solenoid controlled by an electrical sensor switch is used to control the EGR valve
Vacuum suction cup

Dent PullerDent Puller

A hand tool for pulling out shallow body dents and for lifting flat, heavy objects such as windshields or sheet metal

Vacuum suspended power booster
A type of power booster that contains vacuum in both chambers of the booster when the brake pedal is at rest. When the pedal is applied, the rear chamber is vented to the atmosphere, causing the diaphragm of the booster to move toward the master cylinder which assist the driver in the application of the brakes
Vacuum-suspended power chamber
A booster power chamber that has vacuum on both sides of its diaphragm when the brakes are not applied.
Vacuum switch
A switch that closes or opens its contacts in response to changing vacuum conditions.

Vacuum switching valve
(VSV) an electrically controlled vacuum switching valve used to control emission control devices
Vacuum tank
A tank in which a vacuum exists. It is generally used to provide vacuum to a Power brake installation in the event engine vacuum cannot be obtained. The tank will supply several brake applications before the vacuum is exhausted.
Vacuum timing control
Vacuum transducer

Vacuum transducerVacuum transducer

A sensor with a vacuum diaphragm which moves an iron rod inside a coil of wire sending a signal to the computer that is proportional to the amount of vacuum.

Vacuum transmitting valve
(VTV) a valve used to limit the rate of vacuum advance
Vacuum unit
Vacuum valve
Vacuum Valve Assembly
Vacuum vent valve
(VVV) controls the induction of fresh air into a vacuum system to prevent chemical decay of the vacuum diaphragm that can occur on contact with fuel
Vacuum Zone Switch
  1. Abbreviation for Vane air-flow meter
  2. Abbreviation for Volume Air Flow
A panel used to conceal structural detail or to provide extra protection.

Valet parking
The parking of your car by a parking attendant
Valet switch
On some alarm systems, a switch to override the alarm system for valet parking, car washes, etc.
Value added
Value of shipment
Summation of value of shipments produced by establishment, receipts of custom and repair revenue.
A device used to either open or close an opening to allow or prevent the flow of a liquid or gas from one place to another.


Valve actuation
Valve adjusting screw
A screw at the end of a rocker which bears on a pushrod; used to tilt the rocker and thus adjust the valve clearance
Valve and transducer assembly
This type of EGR valve consist of a modified ported EGR valve and a remote Transducer. Works the same way as an integral backpressure transducer EGR valve
Valve angle
A segment of the full circle of a rotary disc valve cut out to admit the fresh charge into the cylinder
Valve aperture
Valve assembly
A device through which a tire is inflated. It includes a valve stem, valve core, and valve cap.

Valve block
Valve body
Part of the valve assembly containing plungers, pistons, springs, etc.
Valve body housing
A housing which incorporates the bores in which the valve spools slide and the canals which channel the oil flow
Valve body separator plate
A plate sandwiched between two gaskets which separates the upper and lower parts of the valve body
Valve bounce
The bouncing of a valve on its seat due to the valve spring resonating at very high engine speeds. Also called flutter.


Valve bushing
Valve cap
A screw-on cap to prevent the entry of dirt and dust into the tire valve. It does not keep the air in — the Valve core does that.
Valve carburetor
Valve clearance
The distance between the small end of the Valve stem and the Rocker arm or Valve lifter. This gap is necessary to compensate for Expansion due to heat. Also called Valve lash.
Valve clearance depression
A recess in the piston crown
Valve closes
Valve core
A check valve within a tire air valve which permits air pressure chucks without undue loss of air pressure. The core should not be considered a valve seal.
Valve cover
A long metal lid located on the top of the cylinder head on vehicles with overhead camshafts. The valve cover is removed when the valves need adjusting. The British term is rocker box or rocker cover.
Valve cover gasket
A gasket between the cylinder head and the valve cover; usually either a flat paper or cork gasket or an O-ring. The British term is rocker cover gasket.
Valve crown
Valve cut-out
On some four-valve engines at low speed the main rocker arms open only two valves per combustion chamber in order to keep the energy of the gases at a high level; with increasing rpm, the energy of the gases becomes sufficiently strong for the remaining two valves to be opened via hydraulic locking bolts
Valve diameter
Intake valves can be distinguished from exhaust valves by their larger diameter
Valve duration
The length of time, measured in degrees of engine crankshaft rotation, that a valve remains open.
Valve engine
Valve, expansion
Type of refrigerant control which maintains constant pressure in the low side of refrigerating mechanism. Valve is caused to operate by pressure in low or suction side, Often referred to as an automatic expansion valve or AEV.
Valve extension
Extra length added to a tire valve stem for greater accessibility particularly on inside duals.
Valve face
The outer lower edge of the Valve head. The face contacts the valve seat when the valve is closed.
Valve float
A condition where the valves in the engine are forced back open before they have had a chance to seat. Brought about (usually) by extremely high rpm. The Valve lifters lose contact with the cam lobes because the Valve springs are not strong enough to overcome the Momentum of the various Valvetrain components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the Valvetrain. Also called Valve bounce
Valve follower
Valve gear
A mechanism that operates the intake and exhaust valves; includes the cams, pushrods, rocker arms, etc. but not the valves themselves
Valve grinder
A special automotive tool consisting of a wooden shaft and rubber suction cup(s) for hand grinding valves.
Valve grinding
Renewing the Valve face area by grinding on a special grinding machine.
Valve grinding compound
An abrasive compound used for refacing valve seats. The suction cup is placed on the valve head and the valve is pressed into the seat; turning the handle between one’s hands will grind the valve into its seat; always use with grinding paste. Not to be confused with valve seat cutter which is used to cut worn valve seats to a specific angle. Also called valve lapping compound
Valve grinding tool
A special automotive tool consisting of a wooden shaft and rubber suction cup(s) for hand grinding valves
Valve guide
The cylindrical hole which is located in the cylinder head or Block through which the stem of the Poppet valve passes. It is designed to keep the valve in proper alignment. It also serves as a bearing surface. Some guides are pressed into place and others are merely drilled in the block or in the head metal.

Valve guide driver
A tool for installing valve guides
Valve guide reamer
A tool used to enlarge worn valve guides to accommodate oversized valve stems
Valve guide remover
A drift punch for driving out valve guides
Valve guide seal
Valve head
The surface of the large end of a valve.
Valve hole
The circular opening in the rim of a wheel for mounting tubeless tires. Tubeless car tires commonly have a snap-in valve consisting of a rubber molding bonded to the metal stem casing. The rubber molding has a groove formed at the base; when the valve is pulled through the valve hole, the pliable rubber base snaps into position. Commercial vehicle valves for tubeless tires are all metal; they are attached to the rim and the valve hole by an extended thread formed at the base and secured by a nut. Airtight sealing is achieved by either an O-ring or a fiat and flanged rubber washer. Commercial vehicle valve stems may have a single, double, or triple bend to accommodate different rim profiles and single and twin wheel combinations. On bicycle rims, the hole may be one of two sizes to accommodate Presta or Schrader valves. Also called valve aperture
Valve induction
Valve induction timing
Valve in head engine
Valve-in-head engine
An engine in which both intake and exhaust valves are mounted in the cylinder head and are driven by pushrods or by an overhead camshaft. Also called I-head engine or Overhead-valve engine.
Valve In Receiver
Valve job
Replacing or regrinding old valves
Valve keeper
A small unit that snaps into a groove in the end of the Valve stem. It is designed to secure the Valve spring, valve spring retaining washer and valve stem together. Some are of a split design, some of a horseshoe shape, etc. Also called Valve key or valve retainer.
Valve key
Key, keeper, washer, or other device which holds valve spring cup or washer in place on valve stem

Valve lag
The time between TDC or BDC and a valve closing
Valve lapper
A special automotive tool for grinding (lapping) valves into valve seats; some types are power-operated, thus allowing faster grinding compared with standard suction-type valve grinding tools
Valve lapping compound
Valve lash
Valve tappet Clearance or total Clearance in the valve operating train with Cam follower on camshaft Base circle.

Valve Lead
The time between a valve opening and TDC or BDC
Valve lift
Distance a valve moves from the full closed to the full open position. It is usually about a quarter of the diameter of the port.
Valve lifter
  1. The cylindrically shaped component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates. Most valve lifters have an oil-lubricated hardened face that slides on the cam lobe. So-called roller lifters, however, have a small roller in contact with the cam lobe — thereby reducing the friction between the cam lobe and the lifter. Also called valve follower or Cam follower.
  2. A tool that compresses valve springs for removal and replacement.
Valve lock
Key, keeper, washer, or other device which holds valve spring cup or washer in place on valve stem
Valve Main Burner
Valve margin
The width of the edge of the Valve head between the top of the valve and the edge of the face. Too narrow a margin results in Preignition and valve damage through over-heating.
Valve oil seal
A Neoprene rubber ring that is placed in a groove in the Valve stem to prevent excess oil entering the area between the stem and the guide. There are other types of these seals.
Valve opens
Valve overlap
A certain period in which both the intake and exhaust valve are partially open. The intake is starting to open while the exhaust is not yet closed. It is usually expressed in degrees of crankshaft rotation and determined by the valve timing, valve overlap is necessary for the efficient flow of gases in and out of the combustion chamber
Valve plate
Part of compressor located between top of compressor body and head. It contains compressor valves and ports.

Valve port
The opening, through the head or block, from the Intake or exhaust manifold to the valve seat.
Valve principle
The original method of ABS control using an electrically operated valve to control the air pressure
Valve Refrigerant Cylinder
Valve retainer
Valve rotator
A unit that is placed on the end of the Valve stem so that when the valve is opened and closed, the valve will rotate a small amount with each opening and closing. This gives longer valve life. Also called Roto cap
Valve seat
  1. The area onto which the face of the Poppet seats when closed. The two common angles for this seat are forty-five and thirty degrees.
  2. The surface against which a valve comes to rest to provide a seal against leakage.
Valve seat cutter
A special automotive tool with carting blades for use with power tools; used to cut worn valve seats with 30° or 45° angles
Valve seat face
An annular part of a valve head located at the valve seat of the cylinder head
Valve seat grinding
Renewing the valve seat area by grinding with a stone mounted upon a special Mandrel.
Valve seat insert
A hardened steel valve seat that may be removed and replaced. The use of valve seat inserts dispenses with the need for lead in the fuel to act as a lubricant between the valve head and seat


Valve seat ring
A ring-shaped insert of a harder metal than that of the cylinder head; the use of valve seat inserts dispenses with the need for lead in the fuel to act as a lubricant between the valve head and seat
Valve, service
Device used to check pressures, service, and charge refrigerating systems.
Valve shim
A calibrated shim used to adjust valve clearance on OHV engines with bucket tappet assembly; for adjustment, a calibrated valve shim is placed or removed from between tappet and cam
Valve shim pliers
A special automotive tool for the removal and installation of valve shims
Valve Shutoff
Valves-in-receiver unit
(VIR) a component used on GM system, in which the thermostatic expansion valve, POA suction throttling valve, the receiver-drier, and, if equipped, the sight glass are all combined into one assembly
Valve slot
Tube-type tires require a valve slot instead of a valve hole to allow the tire valve to be removed from the rim; a thread adaptor is molded to a circular rubber patch vulcanized to the inner tube; the valve stem casing is then screwed onto the tube adaptor
Valve, solenoid
Valve made to work by magnetic action through an electrically energized coil.
Valve spool
  1. In an automatic transmission, a sliding cylindrical internal part of a valve with one or more sections of reduced diameter
  2. A spool-shaped valve, such as in the power-steering unit.
Valve spring
A small Coil spring that closes the valve after it has been opened by the cam, and prevents the valve from bouncing on its seat. The action of the spring keeps the Lifter in contact with the cam. If the spring is weak, noise will be generated and the valve, spring, lifter and cam will be subjected to hammer-like blows that cause Metal fatigue.

Valve spring cap
The retaining cap (of intake or exhaust valves) which secures the valve keeper on the valve stem
Valve spring collar
The retaining cap (of intake or exhaust valves) which secures the valve keeper on the valve stem
Valve spring compressor
A special automotive tool used to compress valve springs for removal and replacement; the most common type is a c-shaped clamp
Valve spring depressor
A lever-type tool used to depress valve springs, e.g., for removal and installation of valve stem seals
Valve spring lifter
A pliers-type tool with two expanding jaws, used to lift and compress valve springs for removal and replacement
Valve spring retainer
Valve spring seat
A seat retaining the bottom of the valve spring
Valve stem
The long cylindrical portion of the valve that moves up and down in the Valve guide.
Valve stem seal
The oil seal between the valve and the cylinder head which prevents excessive oil leakage from the top of the cylinder head into the combustion chamber
Valve stem seal installer
A sleeve-type tool used to push down valve stem seals for installation
Valve stem seal pliers
A special plier for removing valve stem seals on overhead camshaft engines
Valve, suction
Valve in refrigeration compressor which allows vaporized refrigerant to enter cylinder from suction line and prevents its return.
Valve switch
Valve system
Valve tappet
An adjusting screw to obtain the specified Clearance at the end of the Valve stem (tappet clearance). The screw may be in the top of the Lifter, in the Rocker arm, or in the case of the Ball joint rocker arm, the nut on the mounting Stud acts in place of a tappet screw.
Valve Three And Four-port
Valve timing
Adjusting the position of the camshaft to the crankshaft so that the valves will open and close at the proper time.

Valve tip
The upper end of the valve that contacts the rocker arm
Valve train
Valve trainClick image to supersize
Valve train
  1. The various parts making up the valve and its operating mechanism which causes the valves to open and close.
  2. The system of valves that lets the fuel charges in and let the exhaust gases out.
Valve Two-port
Valve umbrella
A washer-like unit that is placed over the end of the Valve stem to prevent the entry of excess oil between the stem and the guide. Used in valve-in-head installations.
Valve Vacuum Motor
Valve, water
In most water cooling units. a valve that provides a flow of water to cool the system while it is running.
  1. A covered road vehicle for carrying goods.
  2. A recreational vehicle based on the body of a commercial van, usually with comfortable, plush interior trim, often with a bed.
  3. A cargo body style with a totally enclosed cargo area. Included are beverage vans, or bay vans, and sealed shipping containers mounted on a special bodiless chassis.
Vanadium Inhibitor
An organic and/or inorganic metal bearing chemical intended to chemically and/or physically combine with the compounds formed during combustion of heavy fuel oil to improve the surface properties of the treated ash compounds.
Van camper
Van conversions
A thin plate that is affixed to a rotatable unit to either throw off air or liquid, or to receive the thrust imparted by moving air or liquid striking the vane. In the first case it would be acting as a pump and in the second case as a Turbine.

Vane air-flow meter
(VAF) a sensor with a moveable vane connected to a potentiometer calibrated to cause the amount of air flowing to the engine
Vane air temperature sensor
(VAT) located inside the vane airflow meter housing; sense the temperature of the air flowing into the engine
Vane-in-rotor pump
A Sliding-vane pump
Vane-in-stator pump
Vane pump
A type of rotary pump with either a slotted rotor and sliding vanes or a rotor with hinged vanes; typically used for air pumps in secondary air injection systems, as a compressor in air conditioning systems, and in some transmission systems.

Vanes compressor
Mechanism for pumping fluid by revolving blades inside cylindrical housing.
Vane switch
Vane wheel impeller
An impeller with straight radial vanes
Vanity plate
A vehicle license plate which contains a series of characters (numbers and letters) which provide personalized identification rather than a random series of characters.

Van lift

Van liftVan lift

A platform which is deployed from a vehicle, allowing people who use wheelchairs or have trouble stepping up easy access. These platforms or lifts are run by electricity or hydraulics but can always be manually operated in the event that one of the previously-mentioned power sources fail.

Vanity mirror
A mirror on the inside of a sun visor
  1. The gaseous form of a liquid which is usually created by heating the liquid.
  2. A gas which is often found in its liquid state while in use.
  3. The gaseous state of refrigerant. Vaporized refrigerant is preferred to the word gas.
Vapor barrier
Thin plastic or metal foil sheet used in air-conditioned structures to prevent water vapor from penetrating insulating material.
Vapor canister
Vapor degreasing
A type of cleansing procedure to remove grease, oil, and loosely attached solids from metals; a solvent such as trichlorethylene is boiled, and its vapors are condensed on the metal surfaces
Vapor deposition
A production of a surface film of metal on a heated surface, usually in a vacuum, either by decomposition of the vapor of a compound at the work surface, or by direct reaction between the work surface and the vapor.

Vapor displacement
The release of vapors that had previously occupied space above liquid fuels stored in tanks. These releases occur when tanks are emptied and filled.
Vapor injection
  1. Breaking the gasoline into fine particles and mixing it with the incoming air.
  2. Change of liquid into a gaseous state.
The action of converting a liquid into a mist or vapor by breaking it into small particles and mixing it with air. The design of the carburetor and fuel injectors vaporizes gasoline to produce a combustible fuel-air mixture. If it is not vaporized, the liquid gasoline may not burn properly and may even hydraulic.
Vapor Lamp
Vapor lines
Air conditioning system lines in which refrigerant is normally in a gaseous or vapor state.
Vapor lock
  1. This is an unwanted condition where bubbles of air form in the fuel line caused by boiling or vaporizing of the fuel in the lines from excess heat. The boiling will interfere with the movement of the fuel and the air bubbles which form will in some cases, completely stop the flow. Sometimes it will cause the Float chamber to overflow which Floods the carburetor and result in an over-rich mixture that can cause stalling of the engine when the accelerator is depressed. Fuels containing alcohol have lower Boiling points and many old-car owners have installed more-powerful electric fuel pumps which overcome vapor lock tendencies of these fuels by pushing them through the air bubble. A wet rag will cool the line and get rid of the problem. To prevent the problem in hot weather, some mechanics wrap tinfoil around the fuel lines to reflect the heat away.
  2. The abnormal condition that occurs when brake fluid contains too much moisture and is overheated, causing the moisture in the fluid to boil. Gas bubbles are formed in the fluid, which causes a spongy brake pedal or a complete loss of hydraulic pressure.
  3. Condition where liquid is trapped in line because of bend or improper installation. Such vapor prevents liquid flow.
Vapor pressure
  1. Pressure imposed by either a vapor or gas.
  2. The tendency of a liquid to pass into the vapor state at a given temperature. With automotive fuels, volatility is determined by measuring RVP.
Vapor pressure curve
Graphic presentation of various pressures produced by refrigerant under various temperatures.
Vapor recirculation
Vapor recirculation system
Vapor recovery
An emission control system used by gasoline stations. A special filler nozzle seals the gap between the pump filler nozzle and the car’s filler opening, preventing benzene vapors from escaping into the atmosphere; instead, they are recycled into the gas station’s own fuel tank; the same system is also used when the gas station receives a new delivery of fuel from a gas tanker

Vapor recovery system
A system that prevents the escape of gasoline vapors from the fuel system into the atmosphere. The basic system consists of a Canister filled with activated Charcoal and pipes connecting the Canister to the fuel tank and carburetor. Any vapor-filled air that leaves the fuel tank because of Expansion passes through special emission control pipes to the Canister where the vapors are grabbed and stored by the Charcoal. Then when the engine is started, intake manifold vacuum draws fresh outside air up through an opening in the Canister. This moving air pulls the fuel vapor out of the Charcoal and carries it to the carburetor and into the engine. In the meantime any gasoline that evaporates from the carburetor collects in the carburetor and Air cleaner. As soon as the engine starts this vapor is drawn down through the carburetor and into the engine along with the entering fuel-air mixture. Also called evaporative emission control.

Vapor recycling
An emission control system used by gasoline stations. A special filler nozzle seals the gap between the pump filler nozzle and the car’s filler opening, preventing benzene vapors from escaping into the atmosphere; instead, they are recycled into the gas station’s own fuel tank; the same system is also used when the gas station receives a new delivery of fuel from a gas tanker
Vapor retarder
A material that retards the movement of water vapor through a building element (walls, ceilings) and prevents insulation and structural wood from becoming damp and metals from corroding. Often applied to insulation batts or separately in the form of treated papers, plastic sheets, and metallic foils.
Vapor, saturated
Vapor condition which will result in condensation into droplets of liquid if vapor temperature is reduced.
Vapor separator
A device used on cars equipped with air conditioning to prevent Vapor lock by feeding vapors back to the fuel tank via a separate line.
Vapor Valve
Vapor withdrawal
A system of piping and connection to operate an engine directly on vapor taken from the top of an LPG tank
British spelling for Vapor
A unit of reactive power in a circuit carrying a sinusoidal current. A VAR equals the amount of reactive power in the circuit when the product of the root-mean-square value of the voltage (volts) by the root-mean value of the current (amps) and the sine of the phase angle between the voltage and the current, equals 1.
Abbreviation for Vacuum Assisted Resin Injection — a process for forming composite panels and bodywork with consistent, controllable results.
Variable air volume
(VAV) system on the heating and cooling system: A means of varying the amount of conditioned air to a space. A variable air volume system maintains the air flow at a constant temperature, but supplies varying quantities of conditioned air in different parts of the building according to the heating and cooling needs.
Variable air volume controller
(VAV) Device having electronic components used to regulate the volume of air in a distribution system.
Variable assist power steering
A power steering system that enables the stiffness or tension of the steering to increase at higher speeds for more control or to soften at low speeds when performing slower activities, such as parallel parking.

Variable assist steering
Variable belt transmission
A continuously variable transmission using rubber V-belts on expanding-contracting pulleys, depending on engine speed and load; originally developed by van Doorne for DAF and then used on the Volvo 340
Variable-choke carburetor
Variable displacement compressor
A compressor which can change its output in accordance with the conditions.
Variable dwell
Variable exhaust port
Variable fuel vehicle
Variable hole cutter
A drill bit with a stepped cutting head used to drill holes into sheet metal and to enlarge the radii gradually by advancing from one step diameter to the next on the same drill bit
Variable intake manifold
A setup in which the path through which air travels into the engine can be altered. Altering the path at a set point allows an engine to develop more power over its rev range.
Variable-jet carburetor
A carburetor with a sliding needle which moves in and out of a jet to change its functioning size. A type found on many motorcycle carburetors.
Variable limited-slip axle/center differential
A limited-slip axle/center differential with an electronically operated multiple-disc clutch as a slip-inhibiting device
Variable message sign
An upright electronic computer-controlled highway information sign sign (either permanent or movable), which reveals road conditions, traffic restrictions, road safety, etc.
Variable pitch pulley
Pulley which can be adjusted to provide different pulley drive ratios.
Variable pitch stator
A Stator that has Vanes that may be adjusted to various angles depending on load conditions. The vane adjustment will increase or decrease the efficiency of the Stator.
Variable rate springs
Springs which become stiffer under compression; variable rate gas springs are a feature of air suspension systems
Variable ratio steering
Steering ratio characteristics in power steering systems providing different ratios for small and large steering angles
Variable reluctance sensor
(VR or VRS) a non-contact Transducer that converts mechanical motion into electrical control signals
Variable resistor
A resistor, connected in series with an electric motor that can be adjusted to vary the amount of current available and thereby alter motor speed
Variable-speed wind turbines
Turbines in which the rotor speed increases and decreases with changing wind speed, producing electricity with a variable frequency.
Variable spring
Spring providing variable effective length through cam action to suit load.
Variable Transducer
Variable transmission
Variable valve actuation
In older engines, the intake and exhaust valves operated in a fixed program of timed openings and closings. With variable valve actuation, these actions are varied for a better balance of low-speed, medium-speed, and high-speed operation.
Variable valve timing
Through the use of computers, the precise time when the valves open and close can be altered. It may be better to change the timing slightly when the engine is at a higher RPM than when it is slower.
Variable-venturi carburetor
The characteristic feature of this carburetor is the vacuum-operated piston which adjusts the cross-sectional area of the venturi and moves a jet needle in and out of a needle jet; typical designs are the SU and Stromberg carburetors
Variable volume induction system intake configuration
A restrictor plate that opens and closes controlling the amount of oxygen that can go into the engine.
Variomatic transmission
A transmission which used rubber belts and expanding pulleys to provide an infinitely variable belt drive.

  1. A deposit on the interior of the engine caused by the engine oil breaking down under prolonged heat and use. Certain portions of the oil deposit themselves in hard Coatings of varnish.
  2. Residue formed when gasoline gets old and stale.
Abbreviation for Vane air temperature sensor
Abbreviation for Vehicle AntiTheft System
VauxhallClick image for books on

A vehicle brand of which only the 25-70 and 30-98 models of the 1925-1948 era are classic cars.

Abbreviation for Variable air volume
Abbreviation for vertical-axis wind turbine
V-band clamp
A clamp which connects the turbine housing and bearing housing
Abbreviation for Vehicle (system) Battery Voltage
  1. A drive belt with a V-shaped cross section, for transmission of low to moderate forces; typically used to drive generators, water pumps, air pumps, air conditioner compressor units and power steering pumps.
  2. Type of belt commonly used in refrigeration work. Has a contact surface with a pulley which is in the shape of a V.
V-belt drive
A type of friction drive in which forces are transmitted from belt to pulley or vice versa by friction
Abbreviation for Vehicle Builders And Repairers Association
A type of ATB brake patented by Shimano. This type of brake is characterized by the brake cable coming at the brake arms from the side (usually through a curved piece of aluminum tubing referred to as a noodle). This type of brake has replaced cantilever brakes on ATB bicycles (as well as tandems and touring bicycles) because the V-Brake has more power and is easier to set up.
VB voltage
Abbreviation for Battery voltage
Abbreviation for Viscous coupling
Abbreviation for Vacuum Cut Control Solenoid
Abbreviation for Vacuum check valve
  1. Abbreviation for Vehicle condition monitor
  2. Abbreviation for Vehicle Control Module
Abbreviation for Variable Control Relay Module
Abbreviation for Vacuum Control Temperature Sensing Valve (Ford)
Abbreviation for Viscous coupling unit.
Abbreviation for Vacuum control valve
Abbreviation for Verband der Automobilindustrie (i.e., German Automakers Association)
Abbreviation for variable displacement orifice tube air conditioning system
  1. Abbreviation for Vacuum delay valve.
  2. Abbreviation for Vacuum differential valve
Value engineering.
Abbreviation for Vehicle Emission Control Information which is on a decal or label placed on the windshield of a car.
A physical quantity which has direction such as force and Momentum.
Vector potential
Potential postulated in electromagnetic field theory. Space differentiation (curl) of the vector potential yields the field. Magnetic vector potential is due to electric currents, while electric vector potential is assumed to be due to a flow of magnetic charges.


Veeder root
The brand name of a common type of odometer.
Vee engine
A type of engine with two banks of cylinders, each set at an angle to each other (in an end view) to form a V.
A clockwise change in the direction from which the wind comes.
Vee thread
Any screw thread having a triangular profile. In 1958, the triangular profile of the Unified screw threads was adopted as the basis of a new international system of screw threads, now known as ISO screw threads. The ISO system of screw threads comprises several metric series (which supersede the S. I. screw threads) and also several inch series (which supersede both the screw threads of Whitworth form and the Unified screw threads).
  1. See Facel Vega
  2. VegaClick image for books on

    A model of car produced by the Chevrolet division of General Motors from 1971-77

  1. A conveyance on wheels or runners used to carry people or goods over land (e.g., bicycle, motorcycle, car, truck, sleigh, snowmobile).
  2. A binder.
  3. The liquid portion of an adhesive, coating, or sealer compound consisting of the binder and volatile thinners.
Vehicle Builders and Repairers Association
(VBRA) A British trade association
Vehicle classification
Vehicle Converter
Vehicle dynamics
The behavior of a vehicle in motion.
Vehicle Emission Control Information
(VECI) a label in the engine compartment, e.g., pasted to the radiator fan cover, providing information about the engine and emission controls
Vehicle fuel consumption
Vehicle fuel consumption is computed as the vehicle miles traveled divided by the fuel efficiency reported in miles per gallon (MPG). Vehicle fuel consumption is derived from the actual vehicle mileage collected and the assigned MPGs obtained from EPA certification files adjusted for on-road driving. The quantity of fuel used by vehicles.
Vehicle fuel efficiencies
Vehicle fuel expenditures
The cost, including taxes, of the gasoline, gasohol, or diesel fuel added to the vehicle’s tank. Expenditures do not include the cost of oil or other items that may have been purchased at the same time as the vehicle fuel.
Vehicle Identification Number
(VIN) Number assigned to a vehicle by the manufacturer primarily for registration and identification purposes (consisting of numerals and letters).
Vehicle importer
An original vehicle manufacturer (of foreign or domestic ownership) that imports vehicles as finished products into the United States.
Vehicle Licensing
Vehicle Licensing Agency
Vehicle Licensing Center
Vehicle Maintenance Reporting Standards
(VMRS) A set of codes developed to facilitate computerized tracking of parts and labor used in equipment repair. Established and maintained by the American Trucking Associations.
Vehicle miles traveled

  1. The number of miles traveled nationally by vehicles for a period of 1 year. VMT is either calculated using two odometer readings or, for vehicles with less than two odometer readings, imputed using a regression estimate.
  2. A unit to measure vehicle travel made by a private vehicle, such as an automobile, van, pickup truck, or motorcycle. Each mile traveled is counted as one vehicle mile regardless of the number of persons in the vehicle.
Vehicle Producer
Vehicle Program
Vehicle registration document
A document which specifies the registered keeper(s) of a vehicle
Vehicle Safety
Vehicle Safety Act
Vehicle speed sensor
(VSS) A detection device in speedometer cluster which sends the vehicle speed information (i.e., how fast the car is traveling) to the electronic control module
Vehicle Standards
Vehicle system
Vehicle tax


Vehicle weight
Vehicle Weight Rating
(V-8) An engine with eight cylinders in two rows of four cylinders with a common crankshaft and shaped in the letter V
V-eight engine

V-eight engineV-eight engine

(V-8) An engine with eight cylinders in two rows of four cylinders with a common crankshaft and shaped in the letter V. It is usually smoother and more powerful than an in-line six-cylinder. The intake manifold is located inside the V. The exhaust manifold is found on each side of the engine. Before fuel economy became an important selling point, V-8 engines were found in the majority of cars produced in North America.

Instrument that measures air speeds using a direct-reading air speed indicating scale.
An early form of bicycle or tricycle propelled by thrusts of the feet against pedals.
  1. The rate of motion in a particular direction.
  2. Quickness or rapidity of motion, swiftness, speed.
Velocity joint
Velocity stack
A device mounted on the carburetor, typically made of polished or gold anodized aluminum, with or without a wire mesh filter; it looks good, provides greater air intake and increases engine performance but reduces engine life due to the intake of unfiltered or badly cleaned air
Velocity universal joint
An oval track, often with wooden flooring, where bicycles race.
Vena contracta
The point of lowest-pressure and highest velocity that’s located 0.030 inch below the venturi’s throat (minimum diameter). The center of the discharge nozzle or the trailing edge of the booster venturi is placed at the vena contracta
V engine
  1. A small aperture designed to provide an outlet from a confined space or a inlet into it. Air vents (which are also used for heating and are sometimes called louvers) are usually situated at the top of the instrument panel pointing upward toward the windshield), in the center of the instrument panel (directing the airflow out into the middle of the passenger compartment), on each side of the instrument panel (sending the air back along the sides to the rear of the vehicle), and in the center underneath the instrument panel (directing air into the front footwells).
  2. A small triangular window for letting air into the passenger compartment.
  3. A passageway or conduit for conveying products of combustion from fuel utilization equipment, or their vent connectors, to the outside atmosphere.
  4. To expel through a vent; e.g., when bleeding air (through a vent valve or bleed screw) out of a diesel fuel system alter running out of fuel.
Vented brake disc
A brake disc that has cooling passages cast or drilled between its friction surfaces.
Vent connector
That portion of the venting system that connects the flue outlet of fuel utilization equipment to the gas vent or single-wall metal pipe.
Vent gases
Products of combustion from fuel utilization equipment plus excess air, plus dilution air in the venting system above the Draft regulator or similar device.
To provide with (fresh) air
Ventilated brakes
A brake setup which allows air to enter to cool the rotor and caliper.
Ventilated discs
Two discs in a disc brake system separated by ribs and channels to allow cooling air to disperse the heat between the discs
Ventilated rotor
A disc brake rotor whose friction surfaces are separated by cooling fins.
  1. A provision of a free or controlled circulation of air.
  2. Forced airflow, by design, between one area and another.
  3. The natural or mechanical process of supplying conditioned or unconditioned air to, or removing such air from any space.
Ventilation air
That portion of supply air which comes from the outside (outdoors) plus any recirculated air that has been treated to maintain the desired quality of air within a designated space.
Ventilation slot
A series of gaps in the wheel disc which allow the passage of air to assist brake cooling
Ventilation System
Ventilation Valve
The act of perforating a textile bias ply tubeless tire above the beads during retreading. Thus air bleeding through the calendering can escape without forming air pockets between plies.
Vent limiter
A means that limits the flow of air from the atmospheric diaphragm chamber of a gas pressure regulator to the atmosphere. This may be either a limiting orifice or a limiting device.


Vent port
Vent slot
A series of gaps in the wheel disc which allow the passage of air to assist brake cooling
Vent Tube
PontiacClick image for books on

A model of automobile manufactured by the Pontiac division of General Motors

VentureClick image for books on

A model of mid-size van produced by the Chevrolet division of General Motors from 1997 to 2005

That part of a tube, channel, pipe, etc., so tapered as to form a smaller or constricted area. A liquid, or a gas, moving through this constricted area will speed up and as it passes the narrowest point, a partial vacuum will be formed. The taper facing the flow of air is much steeper than the taper facing away from the flow of air. The venturi principle is used in the Air horn throat of the carburetor.

Venturi tube
A short tube with a constricted passage that increases the velocity and lowers the pressure of a fluid conveyed through it. The venturi, or choke tube, in a carburetor is used to suck the fuel from the float chamber through a discharge nozzle (fixed jet carburetor) or main jet (variable choke carburetor) into the barrel
Venturi vacuum
A vacuum in the venturi of a carburetor which increases with the speed of the airflow passing through it; an exception are VV carburetors
Venturi vacuum amplifier
(VVA) used with some EGR system so that carburetor venturi vacuum can control EGR valve operation; venturi vacuum is desirable because it is proportional to the airflow through the carburetor
Vent Valve
Vent wing
A small triangular-shaped side window which is located in front of the main front side windows. Vent wings can be swung out into the air stream to improve ventilation inside the car. Also called wind wings.
Abbreviation for Voluntary Export Restraint.


Vernier caliper
A short graduated scale that slides along a longer graduated instrument and is used to indicate fractional parts of divisions, as in a micrometer
Vernier gauge
A short graduated scale that slides along a longer graduated instrument and is used to indicate fractional parts of divisions, as in a micrometer
A process in which car bodies are transported horizontally through the surface treatment plant
Vertical-axis wind turbine
(VAWT) A type of wind turbine in which the axis of rotation is perpendicular to the wind stream and the ground.
Vertical keel
Vertical keiretsu
A keiretsu system with a production-oriented close partnership between a major company (such as Toyota) and many small suppliers which work exclusively and/or constantly for their giant customer within the just-in-time concept
Vertical position
Type of weld where the welding is done on a vertical seam and on a vertical surface.
Vertical tire clearance
The distance between the top of the tread and some part of the vehicle closest above it, after subtracting the axle stop clearance and any increase in tread depth from me existing tire.
VespaClick image for books on

A motorscooter manufacturer

A ship used to transport crude oil, petroleum products, or natural gas products. Vessel categories are as follows: Ultra Large Crude Carrier (ULCC), Very Large Crude Carrier (VLCC), Other Tanker, and Specialty Ship (LPG/LNG).

Veteran car
A car constructed before 1919, especially one made before 1905 Only the latter are permitted to take part in the London-Brighton Commemoration Run
Abbreviation for Vacuum Fluorescent
(V-4) An engine with four cylinders in two rows of two cylinders with a common crankshaft and shaped in the letter V
V-four engine
(V-4) An engine with four cylinders in two rows of two cylinders with a common crankshaft and shaped in the letter V
VF voltage
Battery voltage
Abbreviation for Variable-fuel vehicle
A term used in advertisements, short for very good
A term used in advertisements, short for very good condition


Abbreviation for Vacuum operated exhaust heat control valve

Abbreviation for Viscosity index
Vibration arrester
Soft or flexible substance or device which will reduce the transmission of a vibration.
Vibration damper
A round weighted device attached to the front of the crankshaft to minimize the Torsional vibration.

Vibration mounting
Vicat softening temperature
The temperature at which a flat-ended needle of 1 mm² circular cross section will penetrate a thermoplastic specimen to a depth of 1 mm under a specified load, using a selected uniform rate of temperature rise
Vicat test method
A determination of the softening temperature of plastics
Abbreviation for Vehicle Information Centre of Canada.
A British spelling for a clamping device with adjustable jaws (usually mounted on a workbench) used to grip an object to be worked on. The American spelling is vise.

Vice grips
VictoriaClick image for books on
Crown Victoria

A model of automobile manufactured by Ford

Victoria Convertible
See Convertible Victoria
VigorClick logo for books on

A model of automobile from Acura

Abbreviation for Vehicle Interface Module
Abbreviation for Vehicle Identification Number — a unique combination of numbers and letters assigned by the manufacturer to each vehicle and appears on the vehicle’s registration and title.
Vintage car
  1. A vehicle built between 1916 and 1924 (inclusive)
  2. A car constructed in the period 1919-1930
Abbreviation for Valves-in-receiver unit which is found in some air conditioning systems
Virgin resin
A new resin material which has not been recycled before; needed for high-quality parts
Abbreviation for Variable Induction System
A four-seater in which the two passengers faced the driver. Used around the turn of the century.
A light thermal cracking process carried out on a fuel oil during the refining process to reduce product viscosity without blending.
Visco-control unit
Viscoelastic materials
The most characteristic features of viscoelastic materials are that they exhibit a time-dependent strain response to a constant stress (creep) and a time-dependant stress response to a constant strain (relaxation). In addition, when the applied stress is removed the materials have the ability to recover slowly over a period of time
A device used to determine the Viscosity of a given sample of oil. The oil is heated to a specific temperature and then allowed to flow through a set orifice. The length of time required for a certain amount to flow determine the oil’s viscosity.

  1. A measure of an oil’s ability to pour or be thick. Every container of oil is marked with the viscosity of the oil. Straight weight (also called single viscosity or single weight) oil has a single number like 30 weight. A lower number means the oil is thinner and is particularly good for lower temperatures. A higher number is better for hotter temperatures. Multigrade (also called multiviscosity or multiweight) oil has two numbers like 10W40. When the temperature is low, a multigrade oil like 10W40 will act like a 10 weight oil; but when the temperature increases, it will act like a 40 weight. In this way, a multigrade oil is excellent for all-around driving.
  2. Comparative fluidity or stiffness of liquid adhesives, coatings, and sealers.
  3. Measurement of thickness of oil or its resistance to flow. Viscosity usually varies with temperature.
Viscosity cup
A special cup of conical shape with a calibrated bore at the bottom. When filled with paint, the paint will flow out at the bottom of the cup in a determined time. To adjust the viscosity, thinners are added to the paint until the cup contents flow out in the number of seconds indicated in the paint manufacturer’s instructions
Viscosity index

  1. A measure of how the viscosity of a liquid (especially oil) changes with temperature the higher the VI, the smaller the change of viscosity with temperature
  2. A measure of an oil’s ability to resist changes in Viscosity when heated.
Viscosity index improver
An oil additive which reduces thinning at high temperature, thus improving the VI
Thick and sticky
Viscous coupling
A particular kind of fluid coupling in which the input and Output shafts mate with thin, alternately spaced discs in a cylindrical chamber. The chamber is filled with a viscous fluid that tends to cling to the discs, thereby resisting speed differences between the two shafts. Viscous couplings are used to limit the speed difference between the two outputs of a differential, or between the two axles of a car.
Viscous coupling differential
A limited-slip differential using viscous couplings as slip-inhibiting devices
Viscous coupling unit
(VCU). A unit fitted as standard to all Range Rovers across the center differential (not instead of it) automatically to effect locking of the differential when a significant speed difference between front and rear propeller shafts is sensed. Conceptually it comprises a cylinder attached to the rear prop shaft into which an extension of the front prop shaft is introduced. Discs are attached alternately to the front prop shaft and the inside of the cylinder so that they interleave very closely within the cylinder. The cylinder is sealed at both ends and is filled with a special silicone fluid which has the characteristic of markedly increasing its viscosity when stirred. Thus when one prop shaft rotates relative to the other one – the situation of front (or rear) axle wheel-spin – the fluid increases its viscosity enough to lock the shafts together. When relative rotation ceases the viscosity changes back to its original value and the shafts are unlocked. The viscous coupling unit (VCU) has the advantage of being automatic on both engagement and disengagement and its action is gradual and without shock-loading to the transmission.
Viscous-Impingement filter
An air filter that directs the flow of air through a crooked path of wire or screens coated with a tacky oil.
Viscous mode
An operating condition in a viscous coupling with inner and outer parts rotating at different speeds, in which a torque is transmitted through the coupling, which corresponds to the value of the resultant shearing velocity
Viscous transmission
(VT) A four-wheel drive with a viscous center differential
An American spelling for a clamping device with adjustable jaws (usually mounted on a workbench) used to grip an object to be worked on. The British spelling is vice.

Vise grips
Good visibility means that there are no blind spots for the driver in being able to see the traffic around him and that he is able to see the road in dark or adverse conditions.
  1. A movable, perforated part of a helmet, covering the face but permitting sight and speech through the perforations.
  2. The peak of a cap or helmet to shade the eyes from direct sunlight. Visors were also used above the windshield for the same purpose.
Viton-tipped needle
Special inlet valve carburetor needle with a hardened-rubber tip. Viton-tipped needles are resistant to dirt and conform to the seat even at low sealing pressures
Vitreous enamel
A British term for Porcelain enamel. A glassy material obtained by melting a mixture of inorganic materials; this can then be applied in one or more layers on a metal surface to which it is firmly bonded after firing; typical automotive applications are for badges and trim.
Vitreous enameling
An application of a glass coating to a metal by covering the surface with powdered glass frit and heating it until fusion occurs
Abbreviation for Vacuum Sensor and Vacuum Line Charging solenoid valve
Abbreviation for Very Large Crude Carriers. Tankers between 200,000 and 300,000 dwt.
Abbreviation for Variable Load Control Module
Abbreviation for Vane Meter
V max
Maximum (peak) voltage, in alternating current cycle.
Abbreviation for Vehicle Maintenance Reporting Standards — a set of codes developed to facilitate computerized tracking of parts and labor used in equipment repair. Established and maintained by the American Trucking Associations.
Abbreviation for Vehicle miles traveled A unit to measure vehicle travel made by a private vehicle, such as an automobile, van, pickup truck, or motorcycle. Each mile traveled is counted as one vehicle mile regardless of the number of persons in the vehicle.
  1. Abbreviation for Vacuum Modulator Valve
  2. Abbreviation for Vapor Management Valve (EVAP)


Abbreviation for Variable Nozzle Turbocharger

Abbreviation for Volatile organic compounds
Abbreviation for Volatile Organic Fraction
Voice alert system
A system in a car which audibly announces warning messages to the driver, e.g., Warning! Oil pressure too low
Voice recognition
The ability of a computer to recognize a command spoken by the user; enables a driver to use a car phone without using his hands
Small cracks on an object
A vehicle brand of which the 1925-1948 models are classic cars.
Voiture Legere
A light car, especially a racing car falling between the heavy cars and the voiturette. Term seldom used to describe production cars. Not used after 1914.
Early two-seater Touring car. Name first used by Leon Bollee and then applied to any small car.
  1. Easily evaporated.
  2. A volatile substance is one that is capable of being evaporated or changed to a vapor at a relatively low temperature. Volatile substances also can be partially removed by air stripping.
Volatile liquid
A liquid that is easily evaporated.
Volatile matter
Those products, exclusive of moisture, given off by a material as gas or vapor. Volatile matter is determined by heating the coal to 950°C under carefully controlled conditions and measuring the weight loss, excluding weight of moisture driven off at 105°C.
Volatile organic compounds

  1. Unburned hydrocarbon (HC) portions of gasoline
  2. Reactive gases released during combustion or evaporation of fuel and regulated by EPA. VOCs react with NOx in the presence of sunlight and form ozone.
Volatile Organic Fraction
(VOF) The organic fraction of diesel particulate matter as determined by vacuum evaporation. It may or may not be equivalent to the SOF fraction. Depending on the exact analytical procedure, the VOF may include the organic material (SOF) as well as some of the sulfate particulates which, being composed primarily of hydrated sulfuric acid, are also volatile.
Volatile solids
A solid material that is readily decomposable at relatively low temperatures.
  1. The property of gasoline, alcohol, etc., to evaporate quickly and at relatively low temperatures. For instance, gasoline is more Volatile (has higher volatility) than Kerosene because it evaporates at a lower temperature. Low volatility refers to low RVP, indicating less light hydrocarbons in the gasoline front end. Southern California summer grade gasolines have low volatility. Winter grade gasolines in Michigan are high volatility, or high RVP to make the engine easier to start in sub-zero temperatures.
  2. The tendency of a liquid to pass into the vapor state at a given temperature. With automotive fuels, volatility is determined by measuring RVP.
VolkswagenClick image for books on

(VW) A German car manufacturer. Includes Cabrio (1995-2002), Cabriolet (1979-93), Corrado (1990-94), Eos (2007), Eurovan (1993-2003), Fox (1988-93), Golf (1988-2006), Golf III (1993-95), GTI (1988-current), Jetta (1988-current), Jetta III (1993-95), New Beetle (1998-current), New Cabrio (1999), New Golf (1999), New GTI (1999), New Jetta (1999,2005), New Passat (2001), Passat (1990-current), Phaeton (2004-06), Quantum (1988), R32 (2004), Rabbit (2006-07), Scirocco (1988), Touareg (2004-07), and Vanagon (1988-91)


  1. A unit of electrical pressure or force that will move a current of one Ampere through a resistance of one ohm.
  2. The volt is the International System of Units (SI) measure of electric potential or electromotive force. A potential of one volt appears across a resistance of one ohm when a current of one ampere flows through that resistance. Reduced to SI base units, 1 V = 1 kg times m2 times s-3 times A-1 (kilogram metre squared per second cubed per ampere).
  1. A difference in electrical potential between one end of a circuit and the other. Also called electromotive force (EMF). Voltage causes current to flow. Measured in volts.
  2. Term used to indicate the electrical potential or electromotive force in an electrical circuit
  3. Voltage or electrical pressure which causes current to flow.
  4. Electromotive force.
Voltage circuit
Voltage control
Device used to provide some electrical circuits with uniform or constant voltage.
Voltage drop
  1. The lowering of voltage due to excess length of wire, undersize wire, etc.
  2. Loss of voltage encountered across a circuit impedance. Voltage drop across a resistor takes the form of heat released into the air at the point of resistance.
Voltage reduction
Any intentional reduction of system voltage by 3 percent or greater for reasons of maintaining the continuity of service of the bulk electric power supply system.
Voltage regulator
A device which maintains the correct voltage level in a vehicle’s Electrical system by preventing the circuit voltage from exceeding a predetermined safe value. When the battery needs charging the regulator cuts resistance out of the Generator Field circuit, thus increasing the flow of current in that circuit, with the further result that output is increased. When the battery becomes fully charged, the resistance is cut back into the field circuit so that the charging rate is decreased. As the engine speed increases, the Alternator increases and generates more voltage. Unchecked, the alternator might put out so much voltage that Bulbs and other electrical components might burn out. To a certain extent, the battery acts as a voltage regulator, but it too can be damaged by an Electrical system which does not have an operating voltage regulator.

Voltage reserve
Voltage tester
A screwdriver for testing electrical current, with an insulated blade and handle; a bulb inside the handle lights up if the blade touches a live terminal
Voltage transformer
An assembly for increasing the voltage supplied to the air bag system to 12 volts in case of a drop in battery voltage

A dual-purpose instrument for measuring either voltage or amperage
An instrument used to measure the voltage in a given circuit, in volts.

Volt-ohm Multimeter
The measurement, in cubic inches, cubic feet, litres, etc., of the amount of space within a certain object or area.

Volume car
A mass-produced car
Volume Compression
Volume control
Volume Controller
Volume control screw
An adjusting screw which controls the amount of air/fuel mixture supplied by the idling circuit of a fixed-jet carburetor
Volume Expansion
Volume induction system intake configuration
Volume sampling
Volume Spraying
Volumetric efficiency
  1. A comparison between the actual volume of fuel mixture drawn in on the Intake stroke and what would be drawn in if the cylinder were to be completely filled. In practice, a normally aspirated car engine does not take in an amount of an equal to the displacement, it passes only about 80% of the theoretical charge i.e., volumetric efficiency is 80%; this can be increased by supercharging.
  2. Term used to express the relationship between the actual performance of a compressor or of a vacuum pump and calculated performance of the pump based on its displacement.
Voluntary Export Restraint
(VER) In relation to Japanese manufacturers exporting to Canada (no longer in effect).
Voluntary Restraint Agreement
In relation to Japanese manufacturers exporting to the United States (no longer in effect).
A spiral-shaped case in which an Impeller forces liquid in the direction it should go. Often used in pumps.


Volute casing
A progressively expanding pump casing proportioned to reduce the liquid velocity gradually so that some of the velocity energy of the liquid is converted into static pressure
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A model of automobile manufactured in Sweden. A vehicle brand of which the 1961-67 P.1800S, 2-door Coupe models are milestone cars. Includes 240 (1988-93), 740 (1988-92), 760 (1988-90), 780 (1988-90), 850 (1993-97), 940 (1991-95), 960 (1992-97), C30 (current), C70 (1998-current), Coupe (1991), S40 (2000-current), S60 (2001-current), S70 (1998-2000), S80 (1999-current), S90 (1997-98), V40 (2000-04), V50 (2005-current), V70 (1998-current), V90 (1997-98), XC70 (2003-current), and XC90 (2003-07)

Vortex flow
The whirling motion of the oil in a Torque converter as it moves around and around from the pump, through the Turbine, through the Stator and back into the pump and so on.
Vortex tube
Mechanism for cooling or refrigerating which accomplishes cooling effect by releasing compressed air through a specially designed tube,.
Vortex tube refrigeration
Refrigerating or cooling device using principle of vortex tube, as in mining suits.
Abbreviation for Vacuum Operated Throttle Modulator (Ford)
Voyage Charter
Engaging services of cargo ship for specified trip from one port to another at established tonnage rate.
A pulley with a pair of adjustable cup-shaped discs, used on belt transmissions, to permit adjustment of the effective pulley diameter and transmission ratio.

Abbreviation for Variable Pulse Width Modulated
Abbreviation for Ignition Switched Power
  1. Abbreviation for Variable reluctance sensor
  2. Abbreviation for Voltage Regulator
Abbreviation for Voluntary restraint agreement.
Abbreviation for Vacuum retard delay valve
VR engine
A new engine design a combination of in-line and V-engine, the V-angle being reduced (VR) to about 15°. This results in a block which is shorter than a four-cylinder unit of similar capacity. Unlike conventional V-8 engines, the VR engine is topped by a single cylinder head
Abbreviation for Reference Voltage (from PCM) The power supplied by the computer control unit to some sensors regulated at a specific DC voltage
Abbreviation for Vacuum reservoir
Abbreviation for Vacuum restrictor
Abbreviation for Variable Resonance Induction System
Voltage root mean square; average voltage equal to the maximum voltage multiplied by a constant.
  1. Abbreviation for Variable reluctance sensor
  2. Abbreviation for Vacuum Regulator/Solenoid (Ford)
  1. Abbreviation for Vacuum reducer valve
  2. Abbreviation for Vacuum Regulator Valve (Ford)
(V-6) An engine with six cylinders in two rows of three cylinders with a common crankshaft and shaped in the letter V
V-six engine

V-six engineV-six engine

(V-6) An engine with six cylinders in two rows of three cylinders with a common crankshaft and shaped in the letter V. It is more powerful than an four-cylinder engine and short enough to fit into small cars. The cylinder banks are separated by 60° or 90° angles.

(V-16) An engine with sixteen cylinders in two rows of eight cylinders with a common crankshaft and shaped in the letter V
V-sixteen engine
(v-16) An engine with sixteen cylinders in two rows of eight cylinders with a common crankshaft and shaped in the letter V
Abbreviation for Vehicle speed sensor provides digital signal corresponding to vehicle speed
Abbreviation for Vacuum switching valve
Abbreviation for Viscous transmission
VTEC Valve system
Variable Valve Timing and Electronic Lift Control. Changes intake and exhaust valve timing and lift so that it more closely matches the engine’s changing air-fuel needs. The result is maximum torque at all engine speeds and under all driving conditions.
(V-10) An engine with ten cylinders in two rows of five cylinders with a common crankshaft and shaped in the letter V
V-ten engine
(V-10) An engine with ten cylinders in two rows of five cylinders with a common crankshaft and shaped in the letter V
A triangular screw thread
Abbreviation for Vacuum transmitting valve
(V-12) An engine with twelve cylinders in two rows of six cylinders with a common crankshaft and shaped in the letter V
V-twelve engine
(V-12) An engine with twelve cylinders in two rows of six cylinders with a common crankshaft and shaped in the letter V
Two-cylinder engine layout in which the cylinders form a Vt
V-type compressor
A compressor with its pistons arranged in a V-shaped configuration
V type engine
V-type engine
V-type Engine
V-type engine
An engine in which the cylinders occur in two rows set at an angle to each other with the crankshaft running through the point of the V. The single crankshaft is turned by both banks of cylinders. The angle of displacement is generally between 60 and 90 degrees. Although the most common engines are V-8 and V-6, manufacturers have used V-4, V-12, and even V-16
  1. A chemical reaction which changes the physical properties of elastomers.
  2. The setting of rubber into a solid material by use of moderate heat and sulfur or a sulfur compound.
Process rubber by chemical means, usually in combination with heat, to improve its strength, hardness, elasticity, and to effect bonding to other rubber compounds. Used in the manufacture, repair, and retreading of tires.
Vulcanizing sealer
Abbreviation for Venturi vacuum amplifier
Abbreviation for Variable Voltage Choke (Ford)
VV carburetor
Abbreviation for Vacuum vent valve



V-x engine

A V-type engine with a specific number of cylinders represented by the letter x