Although the smaller four cylinder engines of the low compression, low horsepower variety do not generally use a cylinder head temperature gage, the higher powered, more complex powerplants require a cylinder head temperature gage in order to prevent unwitting abuse by the pilot. If head temperatures are higher than normal during flight, it should not be ignored because there is some reason for it. It may be caused by hot ambient temperatures, a lean fuel metering device at higher than cruise power, bad baffles or leaking cowling, or malfunctioning of the ignition system. Even old and tired engine mounts that allow the engine to sag slightly may cause a change in the air-flow pattern and an abnormal increase in CHT. It is also possible that a mechanical problem may be developing in the engine.
When higher than normal cylinder head temperatures are showing on the gage, the pilot should take steps to bring the temperatures down to the normal operating range in order to keep the remaining flight safe. Head temperatures may be reduced by:
1. Enriching the mixture
2. Adjusting cowl flaps
3. Reducing power
4. Any combination of the above
We suggest that in order to help the mechanic diagnose the problem, the pilot or some member of the crew should make a written record of the engine instrument readings during the above flight condition and present it to the maintenance people.
A first step in diagnosing abnormal cylinder head temperatures would be insuring that the gages are providing accurate readings. If they are, the mechanic can then proceed to check engine baffles that may have deteriorated, proper flow of the fuel metering device, and then other more time consuming checks for ignition or mechanical malfunction.