I have a 1995 blazer that overheats but only when the outside air temperature is over around 90 and up. From 90 to aroun 96 it will heat up to around 220 over that it will go to 240 or higher. I have flushed the system, changed the thermostat, changed the hoses, and checked to be sure the sending unit and gauge were working properly, and had checked the water pump. Any ideas as to what would cause this.

 

Will it only stay cool while moving say down the expressway? If so you either have a bad fan clutch or a bad radiator.

 

It stays cool driving it anywhere as long as the outside air temperature in under 90. Once it goes over that I have problems. I put a new fan clutch on it, I didn't mention that in the original post.

 

You possibly have restrictions of some kind in the radiator itself.

 

Yep if it has coolant in it and the fan is working i would say your radiator is plugged up. If that is not the problem its possible that a cracked head or bad head gasket or something like that could be causing heat issues. But try to fix the simple things first and see. If it still overheats it might be time for a compression and leak-down test to see if the motor is mechanically sound too.

 

If you haven't done a thorough cleaning of the exterior of the radiator and A/C condenser, I would do that next.