I have been drilling bleed holes in thermostats for 30 years. I have seen more shadetrees blow head gaskets due to an air-bound cooling system than I care to talk about. lol

SOME modern engines though have such sensitive temperature sensing equipment that drilling a bleed hole in the thermostat will actually cause a check engine light. I have seen this personally on late model GM stuff.

1950 4100 - unrestored and driven weekly for almost no reason at all.