overheating flathead

[JWL]

First check that combustion gases are not leaking into the cooling system. Next check that ignition timing is not either too advanced or retarded at operating speeds. If all is ok, remove the thermostats and see if anything changes. Report your results. By the way, what heads are you using? It really helps to reduce cooling system heat by raising the compression ratio. If you are using stock heads they can withstand .050 milling cut.

I added an electric fan in front of my a/c condenser for operating in heavy stop and go traffic but never have a problem without the extra fan at cruise speeds. I have stock water pumps on a 276 engine and have been over the Rocky Mountains with the a/c blasting in August and no overheating.