Some thermostats have a "jiggle pin" that allows air to vent while the cooling system is being filled, and closes the hole off as coolant starts to flow when the water pump starts it circulating.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!