A Cylinder Head Temperature gauge (CHT) measures the

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ov ...

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

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 gen ...

. Commonly used on air-cooled engines, the head temperature

gauge Gauge ( or ) 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, es ...

displays the work that the engine is performing more quickly than an oil or water temperature gauge. As the

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. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...

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. In all combustion engines, a great percentage of the heat ge ...

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

s as in cars and air-cooled

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...

s.National Transportation Safety Board (NTSB), Safety Recommendation A-12-007, Engine cylinder assemblies that fail
/ref> ULPower UL260i

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 type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''. Thermistors are divided based on their conduction ...

, which measures the temperature at the cold junction so the gauge can adjust the reading. Low budget gauges do not have this compensating thermistor.

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

See also

References