I have a 91 Z28 with a 5.0 TPI. When I was warming up my car this morning, i noticed that the coolant overflow tank was filing up and overflowing out of the tank. The temp began to climb as well. I didn't notice any coolant leak around my water pump as I thought it was not circulating. Do you think my thermostat is not opening? I touched the top radiator hose and it wasn't hot even though my temp was well over 220 degrees. Any input will be appreciated. Thanks

Sounds like the radiator cap is not holding pressure. Get a new one

was the tank just filling up or was it bubbling?

could b cap or T-stat. worst case is head gasket.

it was just filling up.....I hope everyone is right that it is just the thermostat or radiator cap.

if its just filling up, its probably the cap. Its cheap, give it a try

if its a cap thats not holding pressure it would boil at a lower temp and the top hose would be hot, since the hose is staying cold the tstat is stuck shut.