Preheating engines: Airplane engines versus auto engines

"As the pressure drops inside, the air outside has to enter the
crankcase to equalize the pressure, correct? With the air temp as much
as 200 deg higher inside the engine as outside, that means that a
volume of about half the crankcase of outside air ENTERS the crankcase
during the pressure equalization process. At least that is the way it
seems to me."

But it isn't air in the crankcase during engine operation. It is a
mixture of CO2 and water vapor. Outside air will re-enter only when
the water vapor condenses after shutdown. The amount of water vapor
in the comparatively cool outside air being drawn in is one or two
orders of magnitude less than that in the hot crankcase.