[quote=jimmy six #35]This pertains to the GMC. (I believe any head and size) All of the ones I have used have have two 1/2" pipe tap holes back at #6 and one a little farther forward. For many years I put the my temp guage in the rear one and plugged the one farther forward. At El Mirage and more at Bonneville I always showed high cylinder head temp; more than I wanted. About 10 years ago I spotted a stock 302 in a truck and noticed the rear taped hole fed water to the thermostat housing and the one farther forward went to a temp sender. All of a sudden a light went on in my head and I started plumbing all my stock head engines like this. All my "hot" head problems went away.
I have thought about this too. I wonder if the cylinder head temps are still the same, but there are different temps at different spots on the head. so if a guy changes the location of the thermostat, maybe it was lower all the time in this particular spot, and maybe the rear one is still the same temp as before but you are just taking the reading from a different place.
I dont know...
