CHTs above 400☏ should be considered abusive, and grounds for “doing something right now” to bring them down.īy contrast, high EGTs do not indicate that the engine is under excessive stress. For Bonanzas and Barons, a reasonable rule-of-thumb is that optimum engine longevity is achieved by limiting CHTs to 380☏. That’s why it’s so important to manage the powerplant in a fashion that limits CHTs to a tolerable value. High CHTs generally indicate that the engine is under excessive stress for its own good. EGT measures heat energy wasted during the exhaust stroke, when the cylinder is under relatively low stress.CHT measures heat energy wasted during the power stroke, when the cylinder is under maximum stress from high internal pressures and temperatures.CHT mainly reflects what’s going on in the cylinder during the Otto cycle power stroke before the exhaust valve opens, while EGT mainly reflects what’s going on during the exhaust stroke after the exhaust valve opens: EGTįrom a powerplant management perspective, it’s crucial to understand that CHT and EGT tell us quite different things about what’s going on inside the engine. The one-third that actually makes it to the propeller is reflected on another cockpit instrument: the airspeed indicator. The wasted energy is measured and displayed on a triad of cockpit gauges: oil tempera-ture, cylinder head temperature, and exhaust gas temperature. About half the fuel’s energy goes out the exhaust pipe, while the remaining one-sixth is transferred to the cooling air that passes over the cylinder fins and through the oil cooler. My column last month talked about the fact that our piston aircraft engines convert only about one-third of the energy contained in avgas into useful energy to the propeller. Understanding CHT and EGT These two key measurements can tell us a lot about what’s going on inside our cylinders.
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