I have a new long block. After installing noticed a crack in the radiator. Replaced that. Car ran a bit hot and heater blew cold. Burped it with no luck and lower hose stayed cold. Changed tstat just to find my other one worked fine. Burped again today for around 2 hours until it blew hot at idle. Drive it down the road and as soon as I reached 45 mph heater blew cold again and engine temps started rising again. Any help would be appreciated. No symptoms of blown head gasket.

 

I had the very same issue(s) as you and you have a blown head gasket. Does the car smell like coolant? Is the car noticeable "hotter" on the outside? Did the tail pipe smoke once or more than once? Does your overflow continually rise above the recommended level?

Did you drive the car with the radiator cracked? If so, then all these symptoms lead to a re-build.

 

Thanks for the reply. I feel like it might be that too. I don't have any symptoms of a blown gasket though. I did drive the car a very short distance on my test drive with a cracked radiator. Temp never got more than 3/4 hot though. I guess I will need to pressure test the cylinders. No smoke in pipes, oil in coolant, no coolant in oil.

 

Did you have any of the normal blown head gasket symptoms?