I am currently having a problem with my radiator backfilling into the overflow and then the overflow, well overflowing. I was having this problem before and thought is was the radiator so I replaced it with a new one. I also replaced the thermo, overflow tank, and cap. I drained the entire system and used new. It doesn't happen unless I am out wheelin and the temp gets up to about 190-200. I have a 180 thermo in it because I am running a computer chip. The blazer is 1989 w/350fi at/118,000k. Any suggestions what the problem might be? GOT ROCKS?