Cylinder Head Temperature Gauge
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A Cylinder Head Temperature gauge (CHT) measures the
cylinder head In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern ...
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
of an
engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...
. Commonly used on air-cooled engines, the head temperature
gauge Gauge ( ) may refer to: Measurement * Gauge (instrument), any of a variety of measuring instruments * Gauge (firearms) * Wire gauge, a measure of the size of a wire ** American wire gauge, a common measure of nonferrous wire diameter, especia ...
displays the work that the engine is performing more quickly than an oil or water temperature gauge. As the
engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...
works at high speed or uphill, head temperature will increase quickly. The meter can be
digital Digital usually refers to something using discrete digits, often binary digits. Businesses *Digital bank, a form of financial institution *Digital Equipment Corporation (DEC) or Digital, a computer company *Digital Research (DR or DRI), a software ...
or
analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...
. An
air-cooled engine Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. Air-cooled designs are far simpler than their liquid-cooled ...
requires a steady flow of air for cooling. Most air-cooled engines have thermostats controlling air doors or flaps to help the engine reach operating temperature as quickly as possible. Any failure of the cooling system will cause engine failure via scuffed piston skirts. Air-cooled engines are used in aircraft engine control and other
air-cooled engine Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. Air-cooled designs are far simpler than their liquid-cooled ...
s as in cars and air-cooled
motorcycle A motorcycle (motorbike, bike; uni (if one-wheeled); trike (if three-wheeled); quad (if four-wheeled)) is a lightweight private 1-to-2 passenger personal motor vehicle Steering, steered by a Motorcycle handlebar, handlebar from a saddle-style ...
s.National Transportation Safety Board (NTSB), Safety Recommendation A-12-007, Engine cylinder assemblies that fail
/ref> The CHT sender usually has a K-type
thermocouple A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the ...
that is mounted under the spark plug. The K-type thermocouple is a pair of two dissimilar metals that produce a small voltage signal when heated. The metal closest to the spark plug is called the hot junction and the other, closest to the head, the cold junction. The ring under the spark plug is used to transfer the heat from the plug to the thermocouple. The gauge and cold junction are usually calibrated at room temperature, . Because the thermocouple is calibrated for room temperature, the gauge readings will only be 100% accurate at that engine compartment temperature. If the engine compartment temperature is colder, the CHT temperature will display higher. If the engine compartment temperature is higher, the reading will be lower. The error can be corrected with a cold-junction compensating
thermistor A thermistor is a semiconductor type of resistor in which the resistance is strongly dependent on temperature. The word ''thermistor'' is a portmanteau of ''thermal'' and ''resistor''. The varying resistance with temperature allows these devices ...
, which measures the temperature at the cold junction so the gauge can adjust the reading. Low budget gauges do not have this compensating thermistor.


See also

*
Timeline of motor and engine technology Timeline of motor and engine technology * (c. 30–70 AD) – Hero of Alexandria describes the first documented steam-powered device, the '' aeolipile''. * 13th century – Chinese chronicles wrote about a solid-rocket motor used in warfare. * 1 ...
* Timeline of heat engine technology *
Engine cooling Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple syst ...


References

* *P V Lamarque, "The design of cooling fins for Motor-Cycle Engines". Report of the Automobile Research Committee, Institution of Automobile Engineers Magazine, March 1943 issue, and also in "The Institution of Automobile Engineers. Proceedings XXXVII, Session 1942-1943, pp 99-134 and 309-312. *Julius Mackerle, "Air-cooled Automotive Engines", Charles Griffin & Company Ltd., London 1972. * *P V Lamarque, "The design of cooling fins for Motor-Cycle Engines". Report of the Automobile Research Committee, Institution of Automobile Engineers Magazine, March 1943 issue, and also in "The Institution of Automobile Engineers. Proceedings XXXVII, Session 1942-1943, pp 99-134 and 309-312. *Julius Mackerle, "Air-cooled Automotive Engines", Charles Griffin & Company Ltd., London 1972. Engine technology Engine sensors {{technology-stub