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Operating Temp

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What's the normal operating temp of an air cooled engine and where is it measured?

I just got an infrared thermometer and was playing around after mowing my yard. The coolest temp on my 16hp Briggs Single in my Sovereign was 220 degrees at the base of the oil plan. I know air cooled engines run hotter, but I was a bit surprised.

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First of all air cooled engines have no thermostat to maintain a controlled operating temperature, so the cooling temperature changes with the ambient weather and are not published for obvious reasons. The oil pan temperature is a skin temperature reading and not the actual oil temperature. Actual oil temperature might be 20 to 30 degrees higher then what you are recording. Oil temperature doesn't bode well above 250 deg F. So I am wondering if your cooling fins are plugged.

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The higher temps that air-cooled engines see (especially in warm weather and when grass builds up in the fins) is a good reason to use synthetic oil. They will be OK up to around 300 degrees.

On old air cooled snowmobiles, we used to use a thermocouple under the spark plug. If I remember right, they would read at 300-350 degrees, but I have no idea if that was accurate or not. What we used to do is see where the gauge would read under normal conditions and then worry if it started to read higher.

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