Compression test - Hot or Cold?

[Capt Terry]

Might be a good idea to remove the compression tester while engine is still warm. Probably not an issue on a water cooled engine, but almost couldn't get the tester removed from an air cooled VW after the engine cooled down. The thermal coefficient of expansion for aluminum (if I recall correctly w/o looking it up) is almost twice that of steel at the same temperature. So upon cool down the thread fit will get tighter. Fortunately the thread diameter is small, therefore it would be worse on a larger thread size.