Running Hot
Thread Starter
3rd Gear
Joined: Jun 2003
Posts: 3
Likes: 0
From: Jacksonville Florida
Running Hot
Very new Corvette owner. Have a 1975 conv. Just put a new crate motor in. I am having temp. problems. The radiator is a 4 pass Harrison, it has twin elect. fans, (pulling correctly), water pump came with the engine and is working fine, radiator cap was replaced. The cap lifts after only about 15 mins. on the road. Temp guage reads just over 200. The only thing not up to spec. yet are the exhaust manifolds. I have headers to put on. If the engine is designed to flow more exhaust than the stock manifold will put out can this cause an overheating problem? The engine is 350cid 430hp, cast block alum. heads and intake. Can someone give me a suggestion. (be nice)
Melting Slicks
Joined: Jul 2002
Posts: 3,128
Likes: 3
From: Deltona (son of Deland and DAYTONA) FL
Re: Running Hot (Robert2004)
Welcome! :seeya
It could be an airlock. I fought with mine for a while with that issue. try pulling the t-stat, filling from t-stat hole, themn run with out the stat and see if you have the same problem. Also try starting the car with the cap off, letting it get hot and hopefully expel some air. Add some water when it's hot, then recap it. Don't forget to keep the overflow tank at the correct level or you could suck air back in.
One thing that could cause a pressure build up is cylinder pressure making its way into the cooling system. That could come from head gasket or somewhere.
If the pressure is merely from heating, I'd suggest checking to make sure timing isn't retarded and mixture isn't too lean.
BTW, 200 isn't very hot for these cars. I thought it was when I first got mine, but then I learned that a 79 aux electric fan from the factory doesn't even come on until 238 degrees!
It could be an airlock. I fought with mine for a while with that issue. try pulling the t-stat, filling from t-stat hole, themn run with out the stat and see if you have the same problem. Also try starting the car with the cap off, letting it get hot and hopefully expel some air. Add some water when it's hot, then recap it. Don't forget to keep the overflow tank at the correct level or you could suck air back in.
One thing that could cause a pressure build up is cylinder pressure making its way into the cooling system. That could come from head gasket or somewhere.
If the pressure is merely from heating, I'd suggest checking to make sure timing isn't retarded and mixture isn't too lean.
BTW, 200 isn't very hot for these cars. I thought it was when I first got mine, but then I learned that a 79 aux electric fan from the factory doesn't even come on until 238 degrees!
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: Running Hot (Robert2004)
200 degrees doesn't sound too hot to me... I'm usually running 185 - 200 degrees with my 383/465 HP engine.. As long as you run cooler than 230 degrees - you should be fine...
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Running Hot (Robert2004)
Ya running that much hp through the stock manifold is going to cause a bottle neck at the manifolds. But your temp doesn't seem out of line. What lbs is the cap rated? Seems it most be pretty low to open up when you are at about 200 deg.
