1970 Chevy Nova Custom build overheating

1BIGDUALLY

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1970 CHEVROLET NOVA

Engine Cooling problem
1970 Chevy Nova V8 Automatic

The facts
1970 Nova
TH350 w/shift kit
95 chevy 350 2 bolt main short block
Isky 270 cam
Pete Jackson gear drive
Manley valves and guides
World S/R Torker heads
Edelbrock Performer Intake
Holley 850
MSD 6
MSD Streetfire distributor

I built this motor a few months ago. Had 2 row aluminum radiator and electric fan. The one piece oil pan gasket was leaking, so I lifted the motor and pulled the steering linkage, pulled the pan and replaced the seal with another felpro one piece seal. I finished after dark, and headed home. About 20 minutes into the trip, there was a loud boom, lots of smoke, and the car shut off. About 15 minutes later, it started and I headed to the nearest gas station. I found the distributor had been knocked loose and one of the plug wires had popped off the cap. It had shorted a wire. I replaced the wire and put everything back where it belonged. Since then, when I put the motor under a load, such as going 55+ on the road, it overheats quickly, usually running up to 250 degrees. I have replaced the radiator and fan, going to a 16 inch electric fan and 3 core aluminum radiator. No change. Went to a 165 degree thermostat. No change. Had it tested and the overflow tank had CO2 while running which suggested a blown head gasket. I changed the head gaskets today and still no change.

Any ideas?

1 Reply

HMAC300

MECHANIC
48,601 POSTS

This one sounds like a toughy. There are two things I can think of off the bat. I would rule out the radiator and fan, especially as this happens at above 55 mph. I would go for the water pump impeller slipping on the water pump. I would suggest a pump from n a/c car as they hav different imipellers. Also a thing you can check undre the hood, is to start eh car, and rev the motor to about 3000 rpm an dsee if your BOTTOM radiatior hose is sucking together. If it does this it will decrease the flow of water to your engine and could cause this. The cure of course wjould be to replace the hose or if the original hose had a wiere in it put it back in as this iwhat it was for. I can't think of much more with the description of what you have given which is pretty good.