I also had a problem with over heating in my mr2. I would run my car around and if I stoped the engine for more than 5 minutes and restarted it it would start to over heat regardless of how long it had been running before it cooled off it turned out that the lid on the overflow tank had a hole in it were the tubes went thru it so it would run fine untill it cooled off and sucked air thru the hole insted of water. so if your mr2 is over heating and the overflow tank is full that is were the problem will be at more than likely.( raymoorejr@... for questions)