I just spent the last year upgrading to a rebuilt 1969 Olds 455 with a TH400. Car runs like a scalded ape, but on the highway running 3500 rpm going 70mph the the temp gauges goes dangerously high. back it down to 55mph and the gauge drops where it should be. I have a new 3 row aluminum radiator that is supposed to be good up to 500hp. I was thinking of drilling a couple holes in the thermostat to increase flow at high rpm. Any thoughts or suggestions would be greatly appreciated.



7/9/2016

 

What temp is it reaching?

 

My car acts similarly on the highway when I have the AC on and it's 110+ outside. The temp will creep up into the 210+ range when the engine is over 3200 RPM and will drop back to 190-200 if I back off to under ~2800 RPM.

I think the issue is that the cooling system can't dissipate as much heat as the engine is making at the higher RPM. I have a 4-row copper-brass radiator and it works well enough that I just drive slower on the highway during the summer. I don't think drilling holes into the thermostat will help, but a high flow thermostat would probably be a better option. I don't know if that will be enough to cure the issue, though.

 

This is nothing wrong with this temperature, and it is not the indication of an overheating engine. Your engine could run all day long at this temperature with no problems at all. It would be more efficient, and you'd likely get a tiny bit better gas mileage.

 

Define "dangerously high."

 

I agree but I should also say I never tried to see how high it would go; I always back off the RPM when the temp gets to 220. It is possible it would go even higher but I have no desire to verify that.