Automotive Glossary of Terms - V -
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Definitions for automotive terms and illustrations from vacuum advance to voltmeter.
VACUUM ADVANCE: A device which advances the ignition timing in response to increased engine vacuum.
VACUUM MODULATOR: A device used to control the transmission shift points based on the amount of load placed on the engine.
VACUUM GAUGE: An instrument used to measure the presence of vacuum in a chamber.
VALVE: A device which control the pressure, direction of flow or rate of flow of a liquid or gas.
VALVE CLEARANCE: The measured gap between the end of the valve stem and the rocker arm, cam lobe or follower that activates the valve.
VALVE GUIDES: The guide through which the stem of the valve passes. The guide is designed to keep the valve in proper alignment.
VALVE LASH (CLEARANCE): The operating clearance in the valve train.
VALVE STEM SEALS: Synthetic rubber seals that are used to control the oil that lubricates the valve stems in the valve guides. Worn valve stem seals can cause blue smoke from the exhaust when first starting the engine.
VALVE TRAIN: The system that operates intake and exhaust valves, consisting of camshaft, valves and springs, lifters, pushrods and rocker arms.
VAPOR LOCK: Boiling of the fuel in the fuel lines due to excess heat. This will interfere with the flow of fuel in the lines and can completely stop the flow. Vapor lock normally only occurs in hot weather.
VARNISH: Term applied to the residue formed when gasoline gets old and stale.
VCM: See Electronic Control Unit (ECU).
VISCOSITY: The ability of a fluid to flow. The lower the viscosity rating, the easier the fluid will flow. 10 weight motor oil will flow much easier than 40 weight motor oil.
VOLT: Unit used to measure the force or pressure of electricity. It is defined as the pressure needed to move one amp through a resistance of one ohm.
VOLTAGE REGULATOR: A device that controls the current output of the alternator or generator.
VOLTMETER: An instrument used for measuring electrical force in units called volts. Voltmeters are always connected parallel with the circuit being tested.