Techincal Car Terms

Car Dictionary

List of techincal words and terms that your mechanic would usually mention.

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A valve is a device that is controlled mechanically or electrically to meter or prevent the flow of a liquid or gas. Most internal combustion engines use intake and exhaust valves to control the flow of the air/fuel mixture into the combustion chamber and to exhaust burned gases. Some engines have up to four valves per cylinder to increase efficiency and performance. Valves are used in other automotive applications as well. Cooling systems, transmissions, and air conditioning systems use valves where metering of a liquid or gas is necessary.


The valve body is the brain of the transmission. Up and down shifting is controlled by the valve body through hydraulic pressure and electronic commands from the vehicle's performance system. The valve body directs the flow of transmission oil to where it is needed in order for the transmission to perform a function (for example, the application of "passing gear"). The environment within which the valve body operates must be sterile. Varnish buildup and wear material can clog the valve body, causing erratic shift patterns of the transmission. This is why the transmission fluid and filter should be changed every 30,000 miles.


The components which cause the valves to open and close, including the camshaft, tappets (or, cam followers), pushrods, rocker arms, valve springs and valves.

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