Installing Bob Shewmans thermostats

[Old Henry]

Originally Posted by quickchange34

With any thermostat you install always drill a 1/8 inch hole in the middle of the outer ring. It allows a little water through and prevents air lock.

Originally Posted by glennsanders

Just asking,why are they not made with a hole

The current stock replacement thermostats do have a vent hole with a "jiggle pin" in them to shut them off after the cooling system is filled and the engine is running.

Vent open for filling:



Vent closed when water pumping:



The Stant thermostats that I use and recommend have a notch in the valve plate that lets the air through when filling. It is visible in this photo of the Stant on the right. Left is the current stock replacement stat just showing the comparison of the openings in each for water to flow through - the Stant obviously bigger.