Vehicle:
04 Blazer 4x4 4.3 138k-ish miles

She's overheating on me... again.. I just replaced the thermostat, and changed the coolant. I had a 300mile drive today and it was 95-96(according to overhead display) so I wanted to use the AC which I normally don't. I prefer windows down. But she would start really heating up when driving down the interstate when turning on the AC. It'd also heat up some, from about 215ish up to about 220ish going up a some what steep and long hill. I'm thinking possibly fan clutch? Help please!!

 

If you flushed each cooling system component separately, there are no restrictions, (radiator is not clogged etc) the thermostat is new, (and good) and the cooling system is full, at highway speed the fan clutch shouldn't be engaged, it should free-wheel. If it's engaged, or partially engaged, it will restrict air flow through the radiator and cause engine temp to rise.

This fan clutch: Buy Imperial Fan Clutch - Severe Duty 215158 at Advance Auto Parts_____ will howl when cold, but it definitely does the job.

 

When sitting stopped, if I turn the AC on and then I go, I don't hear any difference in the fan than if I didn't have the AC on. That's why I am maybe thinking the fan clutch. Anyone with a better way of testing this? Or any other ideas?

 

Learn about how the fan clutch works from howstuffinmycarworks

Your fan clutch is in need of replacement

 

get rid of it and put a electric fan

 

Way more money, fooling around, stuff to go bad, and maintenance, than it's worth.

 

Man, I hope it is just the fan clutch... Would that also cause the AC not to run as cold as it should? Just had the compressor changed maybe 3 months ago now and the AC just doesn't seem as cold as it could be. Idk if they didn't tighten a line or if there is another leak somewhere.

 

A/C is the removal of heat, not the addition of cold. Gotta get rid of the heat. So if the cooling system is not maintaining the proper coolant temperature, especially air flow through the condenser & radiator, A/C performance will suffer. Stick that fan clutch in post #2 on there

 

Haha yessir!

 

I would also change your rad cap if it is original. They are cheap and can cause you to overheat.

I personally have never had any luck with aftermarket fan clutches and I have tried several. If it were me I would go with an OEM one but that is your call.