While out on a highway trip on Monday my blazer got into the red when I came to a stop. Of course it cooled back down when the truck got some air moving throught the radiator again. I pulled over to check and see what might be the problem and noticed that the overflow tank had overflowed. I have just replaced the water pump and thermostat in the last 2 weeks. Do you think this might be a radiator problem? It is the original and never has been roded out. It looks as if it might be a little corroded inside. It is a 1989 with a 350fi and auto trans. It has 117.000 miles. I can put a new one in, but I want to be sure this might be the problem. Does anybody know what the orig. core size this is, and if I can upgrade to a better one? Thanks for the reply. GOT ROCKS?