Exhaust gas temperature in aviation denotes the temperature of the gases as they pass the exhaust manifold or leave the turbine unit. EGT is measured by temperature-sensing probes located just downstream of the exhaust valve, and on a turbojet the same parameter is sometimes labelled Turbine Outlet Temperature. The reading is presented on an exhaust temperature gauge in the cockpit, forming one member of a triad that includes oil temperature and cylinder head temperature, and it serves as an indicator of wasted energy.
Because EGT determines engine performance and reveals engine fettle, pilots watch it closely. A non-afterburning jet typically shows 600-650°C, while a rise of 20-60°F above the normal 1,400-1,500°F range signals distress. The exact value depends on many parameters, but the principle is simple: EGT offers a direct window onto the thermal state of reciprocating or turbine power plants.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the exhaust temperature of an airplane?
High bypass turbofan exhaust gas temperature is usually around 500-600°C (932-1112°F). Jet engine without afterburner exhaust gas temperature is around 600-650°C (1112-1202°F), while with afterburner the gas reaches up to 1500°C (2732°F). Moving parts, notably exhaust valves, are exposed to temperatures around 1500°F (816°C). Exhaust pipes radiate temperatures in the range of 1200°F (648.9°C) while adjacent areas reach 340°F (171.1°C). The temperature of the engine is determined by the materials used.
What is an aircraft exhaust gas temperature gauge?
An aircraft exhaust gas temperature gauge is used by pilots to monitor the airplane's air to fuel ratio, and exhaust temperature gauges reveal the temperature of the reciprocating engines' exhaust gases.
An exhaust gas temperature gauge - EGT gauge or EGT sensor - is a meter used to monitor the exhaust gas temperature of an internal combustion engine in conjunction with a thermocouple-type pyrometer. In light piston airplanes the gauge is an indicator that reveals the temperature of the airplane's exhaust gases. The EGT gauge tells the pilot the temperature of the exhaust gas, which is an indication of the fuel mixture coming out of the cylinder after the combustion process occurs. It is therefore displaying the average of a relatively cool temperature when the exhaust valve is closed and the spike in high temperature when the valve is open. Modern EGT gauges present numerical temperatures (absolute values) in degrees Fahrenheit or degrees Celsius on the flight-deck gauge instead of the tick marks representing twenty-five-degree increments used by early instruments.
The EGT sensor itself is a temperature-sensing thermocouple-type pyrometer probe located a few inches beyond the cylinder's exhaust port, mounted in the exhaust manifold or immediately after the turbine outlet of a turbocharger. The probe is connected to a gauge located a safe distance away from the high-temperature source, and it reports exhaust probe temperature to the cockpit. In turbine engines the gas temperature is measured by a number of thermocouples mounted in the exhaust stream, and the same arrangement is used for piston engines. The gauge allows pilots to monitor the airplane's air-to-fuel ratio and to set the mixture to a specific ratio that is stoichiometric (peak EGT), richer than stoichiometric (ROP), or leaner than stoichiometric (LOP) by reference to the peak EGT observed when the mixture control is leaned until the maximum EGT is reached.
Because EGT is an indication of how much energy is being wasted out the exhaust pipe rather than being extracted as mechanical energy, the gauge is used to prevent damage to air-cooled engines, assess engine efficiency, and warn of combustion issues, compressor or turbine damage, or fuel-system problems when values are far outside normal ranges. The EGT margin - the difference between the engine's EGT during a full-rated takeoff at reference conditions and the manufacturer-set EGT limit - provides a safety limit, and exceeding that EGT red line results in engine damage or failure.
