He is likely referring to the thermostat bypass hole. The Vortec heads do not have that hole drilled in them, as the Vortec engines use a different style of bypass. The couple engines I have installed Vortec heads on, I did not know about the hole not being there. So consequently I did not drill the hole. I haven't noticed any issues with those engines, but the next time I install a set of Vortec heads, I think I am going to drill that hole. You can find where is comes out on the deck surface, by running a wire up thru the bypass hole on the water pump mounting surface. You could also accomplish this with compressed air.
Some guys say to just drill a couple small holes in the thermostat itself. Maybe two 1/8" holes.
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Originally Posted by ol'blazer
one more question, today a buddy of mine told me that i had to drill a 5/16 hole for the water flow. anybody know anything about this?
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