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I have a 69' 3 door Chevy burb. I just put serpetine drive, a new reverse flow water pump, new performer intake/gaskets etc, flex fan, and temp sending unit. The serpetine drive came out of a 1990 350 from a chevy suburban. I have changed the themastat twice and it is still running hot on the hwy. Idling in the drive way is no problem...it doesn't run hot until you get on the hwy. I'm not sure why...Any thoughts??
Read through this article....
http://www.crankshaftcoalition.com/w...cooling_system
Had the same problem in a serpentine changeover that I did.....the fan blade is the wrong direction...you need a serpentine blade which is made to rotate the opposite direction. Mine idled all day without overheating but when I got on the road, it overheated. One day, I was
standing in front of the truck with the hood up and the air was blowing out of the grille towards me....hmmmm. When it was sitting still, the air didnt care which direction it was going but at highway speeds, the air coming in conflicted with the fan trying to push the air forward. Simple solution is to drive in reverse OR buy the right fan blade.
mike in tucson
By the way, look at the blades from the serpentine fan that came off the enging and then look at your flex fan blades.....pitched the opposite direction are'nt they? GM sells several flex fans (metal blades) which should work.... I assume you went to the flex fan because of the thermostatic fan's length.
mike in tucson
Your sending unit on the manifold or side of the head? Either way I would shoot the area with a hand-held infrared to confirm actual temp because you might be getting cavitation around your sender thereby giving a false reading.
Sounds like the fan may be the problem. Use a OEM fan if possible. GM and Ford spent millions on research. Do you have a shroud? A shroud will help cool the whole radiator. Good luck and keep us updated.