Radiator Glossary of Terms
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Hall Effect
A phenomenon in which voltage is generated by the action of a magnetic field acting on a thin conducting material, commonly used to control the primary circuit of an electronic ignition system. Named for the American scientist, Edwin Hall (1855-1938). The
Halogen Headlights
A type of headlight that produces more light than an ordinary headlight. A halogen bulb burns brighter because it has a thinner filament. To keep the filament from melting, however, the gas mixture inside the bulb is altered slightly by adding a small amo
Head Pressure
Same as "discharge pressure" in an A/C system, the amount of pressure in the compressor discharge line.
Heat Dissipation
The process whereby braking components rid themselves of heat caused by friction. The heat in a disc system is mostly dissipated into the surrounding air. Dissipation can be accelerated by various forms of ventilation.
Heat Range
The measure of a spark plug's ability to dissipate heat from its firing end. The higher the heat range, the hotter the plug fires.
Heat Riser
A channel in an intake manifold through which exhaust gas flows in order to heat the manifold, thus aiding in fuel vaporization. Commonly used in V6 and V8 engines.
Heat Riser Valve
A control valve between the exhaust manifold and exhaust pipe on one side of a V8 or V6 engine that restricts the flow of exhaust causing it to flow back through the heat riser channel under the intake manifold. This aids fuel evaporation and speeds engin
Heat Spots
Shiny dark areas on a rotor caused by extreme heat.
Heated Air Intake System
A system that maintains intake air at a more or less constant temperature by blending outside or underhood air with heated air picked up from a shroud over the exhaust manifold. A typical version uses a vacuum motor to power a door in the air cleaner snor
Heater Core
A water-to-air heat exchanger that provides heat to the passenger compartment airstream. Hot coolant from the engine circulates through the tubes in the heater core.
Helper Springs
Auxiliary springs that increase a suspension's load carrying capacity. These are typically bolt-on springs with a progressive action that do not come into play until the vehicle is loaded or the suspension deflects past a certain point. May be leaf or coi
Herringbone Pattern
Pattern found on the surface of a disc that has been poorly machined.
High Pressure Lines
The refrigeration lines between the compressor outlet and orifice tube or expansion valve. The two longest high pressure lines are the "discharge" and "liquid" lines.
High Side
Same as "discharge side" in an A/C system, the part of the refrigeration circuit between the compressor outlet and orifice tube or expansion valve.
High Side Pressure
Same as "discharge pressure" or amount of pressure in refrigerant liquid line.
Hoop Strength
The retention strength inherent in the belt construction of a tire that resists centrifugal force and provides dimensional stability.
Horsepower
A unit of measure for quantifying power output. Invented by James Watt, the term was originally used to describe how much effort a horse exerted when lugging coal out of a coal mine. One horsepower was the amount of effort one horse put forth in raising 3
Hot Idle Compensator
A temperature-sensitive carburetor valve that opens when the inlet air temperature exceeds a certain level. This allows additional air to enter the intake manifold to prevent overly rich air/fuel ratios.
Hub
The center part of a wheel or gear.
Hub Centric
A wheel that is centered or located on the hub by a machined center hole-as opposed to "lug centered" wheels that are located by the position of the lug nuts alone.
Hub Nut
The large hex nut on the outer end of a front-wheel drive halfshaft that holds the shaft within the wheel hub. Most vehicle manufacturers recommend replacing this nut if it is removed for CV joint service.
Humidity
The amount or percentage of moisture in the air. This affects the perceived cooling performance of the A/C system, and also causes condensation to form on the inside of the windows on cold or rainy days.
HVAC
Acronym for "Heating, Ventilation and Air Conditioning."
Hydraulic
Relating to when a quantity of fluid is forced along one end of a line, exerting pressure at the other end. Since fluids cannot be compressed, when forced into a smaller cylinder, they exert a great amount of force. This technology is used hydraulic brake
Hydraulic System
The delivery system of a modern braking set up. It uses fluid to transmit the force applied at the pedal to the wheel cylinders, where it can be converted back into mechanical energy to activate the brake shoes or disc calipers.
Hydrocarbon (HC)
Any chemical compound made up of hydrogen and carbon. A major pollutant formed by the engine as a byproduct of combustion.
Hydrodynamic Lubrication
Lubrication system where moving engine surfaces are actually separated by an oil film, eliminating all metal contact. Also referred to as "full film" lubrication.
Hydrometer
An instrument used to measure the specific gravity of a solution.
Hydroplaning
The accumulation of water in a film under the footprint which causes a tire to lift from the road surface, losing traction. Hydroplaning is affected by vehicle speed, tread pattern, and water depth.
Hygroscopic
A characteristic whereby something tends to absorb water. Brake fluid is hygroscopic.

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