Quote:
Originally Posted by 64shortbox
It will let the air bleed past the thermostat as you fill the radiator and it also lets a small amount of water past the thermostat as the motor is warming up so your thermostat will open up a little sooner.
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I also drill the hole, simply to let the air escape when filling the system with coolant.
IMO it does not open the thermostat sooner, if anything it opens it later. The water that goes past thermostat will allow fresh water into the engine from the radiator. Of course the fresh water from the radiator is cooler than the hot water in the engine. All that aside I really don't think that little hole makes much of a difference if any in when the thermostat opens.