Hi Matthew

Are you asking if you should test run an engine with a prop on? The answer is yes, always! The prop is needed both for cooling, as you suggested, but also to provide a load on the engine. Too little prop, and the engine will over-rev at full throttle. too big of a prop, and it will struggle to turn it, and probably overheat. Usually, the manual will suggest a prop size for breaking in an engine.

Sandy T