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Heat Range

The measure of a spark plug's ability to transfer heat from the tip of the insulator into the cylinder head.

Heat Riser

A channel in an intake manifold through which exhaust gas flows in order to heat the manifold, thus aiding in fuel vaporization.

Heat Sink

1. A finned, aluminum housing that dissipates heat and serves as a base on which electrical components, such as semiconductor devices, are mounted. 2. A heat dissipating section of the alternator that holds the insulated diodes or all the diodes, and carries heat away from the devices.

Heat Tab

A small aluminum disk attached to the cylinder head or block having a lead center designed to melt at 260 degrees F (127 degrees C) to indicate if the engine has been overheated.

Heat Transfer

The movement of heat from a hotter to a colder area by conduction, convection, or radiation.

Heat Treatable

A metal alloy that can be hardened by heat treatment after being shaped.

Heat Treatment

A sequence of controlled heating and cooling operations applied to a solid metal to provide the desired properties.

Heat-control Valve

A thermostatically controlled valve in the exhaust manifold to divert heat to the intake manifold before the engine reaches normal operating temperature.

Heat-riser Valve

A control valve between the exhaust manifold and exhaust pipe that restricts the flow of exhaust, causing it to flow back through the heat-riser channel under the intake manifold. It acts as an aid to fuel evaporation and to speed engine warm-up.

Heat-shrink Tubing

Tubing that literally shrinks when heated. It often is used to seal connections in vehicle wiring.

Heated-air System

A term used for heated air-intake system.

Heated-air-intake System

A vacuum operated power door in the air-cleaner snorkel that maintains intake air at a near constant temperature by blending ambient air with heated air picked up from a shroud over the exhaust manifold. Also known as heated air system.

Heated-exhaust Gas-oxygen Sensor (HEGOS)

An oxygen sensor that is heated electronically and by engine exhaust so it warms up to normal operating temperature more quickly, allowing the engine to enter closed-loop operation sooner than with a non-heated sensor.

Heater

A device used to warm the vehicle interior.

Heater Core

A small water-to-air radiator-like heat exchanger that provides heat for the passenger compartment.

Heater Valve

A manual or automatic valve in the heater hose used for opening or closing, providing coolant flow control to the heater core.

Heating

The use of an apparatus that produces a relatively high degree of warmth under controlled conditions, by natural or mechanical means, as an aid to ensure personal safety and comfort.

Heating Value

The measure of heat released when a fuel is burned.

Heavy Duty (HD)

A device or product that is designed for heavy use.

Heavy Duty Manufacturers Association (HDMA)

A trade association of original equipment and aftermarket manufacturers of parts, tools, and equipment for servicing heavy trucks.