Matchmcb, there are only three things the will cause an engine to overheat in the air. (I am assuming that it dose not overheat on the ground). First; the needle valve is set at peak RPM on the ground and when the plane is put into a clime it will go a little lean. At first this may not be noticed, but as the plane is flying through a few beautiful maneuvers the engine is going lean each time the nose is above the fuel tank and the engine is getting hotter and hotter, but still not hot enough for you to hear a problem. Also as the flight goes on the fuel level in the tank is getting lower and lower and this also causing the engine to get leaner. If this is your problem the cure is to set the high-speed needle at 300 to 500 RPM rich when the tank is only 1/3 to ½ full, not a full tank. When you fill the tank the engine may be 400 to 600 RPM rich but do not touch the needle. The engine should not go lean in the air and over-heat.

Second; if the engine is in a plane with a cowling it can overheat if not enough cooling air is going over the engine and straight out. The rule of thumb is that the outlet opening must be at least two or three times the area of the inlet opening and (this is important) the cooling air must pass over the hottest parts of the engine and then exit the cowl. Often cowlings trap the hot air and engines overheat because the air inside the cowling is getting hotter. If this is the problem then build a duct or baffle so that cooling air goes in, over the hot engine and straight out. Don’t let hot air swirl around inside the cowl.

The third thing is bad fuel. What is bad fuel? I don’t know. All I know is that when I throw it away my engines run better and cooler.

oldbob