Automotive Glossary of Terms - H -
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Definitions for automotive terms and illustrations from halogen to HVAC.
HALOGEN: A special type of lamp known for its quality of brilliant white light. Originally used for fog lights and driving lights.
HEADER TANK: An expansion tank for the radiator coolant. It can be located remotely or built into the radiator.
HEAT RANGE: A term used to describe the ability of a spark plug to carry away heat. Plugs with longer nosed insulators take longer to carry heat off effectively.
HEAT RISER: A flapper in the exhaust manifold that is closed when the engine is cold, causing hot exhaust gases to heat the intake manifold providing better cold engine operation. A thermostatic spring opens the flapper when the engine warms up.
HEATER CONTROL VALVE: The device that controls the flow of hot engine coolant through the heater core.
HEMI: A name given an engine using hemispherical combustion chambers.
HORSEPOWER: A measurement of the amount of work; one horsepower is the amount of work necessary to lift 33,000 lbs. one foot in one minute. Brake horsepower (bhp) is the horsepower delivered by an engine on a dynamometer. Net horsepower is the power remaining (measured at the flywheel of the engine) that can be used to turn the wheels after power is consumed through friction and running the engine accessories (water pump, alternator, air pump, fan etc.)
HUB: The center part of a wheel or gear.
HYDROCARBON (HC): Any chemical compound made up of hydrogen and carbon. A major pollutant formed by the engine as a by-product of combustion.
HYDROMETER: An instrument used to measure the specific gravity of a solution.
HYDROPLANING: A phenomenon of driving when water builds up under the tire tread, causing it to lose contact with the road. Slowing down will usually restore normal tire contact with the road.
HVAC: Heating, ventilation and air conditioning system.