Prior to operating the engine, provided it is at ambient temperature, the cylinder head temperature indicator will indicate the free outside temperature—a good test for determining that the instrument is working correctly. A check to see that cylinder head temperature is near ambient temperature (cool engine) should be part of the pilot's pre-start procedure. Most cylinder head gauges work without the master switch on because thermocouples generate their own current.

Excessive cylinder head temperature (CHT) can be caused by high power settings (greater heat generation), low airspeed (less cooling), incorrect fuel (lower-than-specified grade), a mixture that is too lean (no excess fuel to evaporate and cool the cylinders), or a low oil level. The cylinder-head temperature gauge should be monitored throughout the flight (especially with high power settings during takeoff, climbs and slow flight) and also on the ground when cooling will be poor. If excessive cylinder-head temperatures are noted, engine cooling can be improved by opening cowl flaps fully, making the mixture richer, reducing the engine power, or increasing the airspeed. In most aircraft, climbing at airspeeds greater than Vy improves engine cooling. Air cooling is least effective at high power and low airspeed, such as on takeoff or go-around.

Pre-ignition and detonation will both cause a rise in CHT with a corresponding decrease in exhaust gas temperature (EGT). The exhaust gases are cooler because the premature ignition causes most of the heat to be released to the piston and cylinder. Pre-ignition results when a hot spot in one or more cylinders causes the fuel/air charge to ignite in advance of the spark. Detonation affects all of the cylinders simultaneously when they become overheated due to a mixture that is too lean, an improper grade of fuel or time-expired fuel, operating the engine with high manifold pressures and low RPMs, or extended high power settings and ground operations. Overheated cylinders "detonate" the fuel/air mixture in advance of the spark.

IF YOU HAVEN'T BEEN MONITORING CHT AND EGT DURING FLIGHT, YOU WON'T KNOW IF THEY HAVE BEEN INCREASING OR DECREASING.

If individual CHT and EGT gauges are not available for each cylinder, it will be difficult for the pilot to distinguish between pre-ignition and detonation and the best course of action will be to correct for detonation first by enriching the mixture (too rich is preferable to too lean).