Here's some background, I have a 96 Blazer 4 door 4WD, I am having overheating issues during the summer when running the AC for over ~30mins. Most of the issues seem to have started when the intake manifold gasket went out 2 years ago. Since then I have done the following:
-replaced intake manifold gasket
-flushed cooling system (replaced with the green all colors coolant)
-replaced thermostat (previous one failed)
-replaced waterpump (previous one failed)
-replaced fan clutch (replaced with a used one, I don't think the old one was bad but I thought I would try it)
-radiator (don't think the old one was bad but I thought this was the last thing that could be causing my problem)

Once the temp starts to go up (moves slowly up) it doesn't matter if I am in rush hour or driving down the highway. Once I turn the AC off, then the temp starts to go back down to normal.

A few years ago I had the AC compressor replaced, it works great but could there be a problem with it that would be causing the engine to work a lot harder?

Any ideas on other things to check or try would be greatly appreciated, I am not sure what to do next.

Thanks,
Todd

 

Hmmm, strange that it still overheats when cruisin down the highway.... What is your definition of 'overheat'? What is the outside air temp?

There could be an issue with your pump such as bad bearings etc... but the fact that it is on at all is causing your engine to work harder. See how hard it is to turn the pump over by hand. Might give you an indication. If it's really hard, and feels gritty - might just be bearings. Any unusual noises when the AC is on??



Aaron

 

Whats the temp when it overheats ?

Over 210 ?

These trucks love to run on 200 i know that

I towed a trailer with 2 mowers and i had the ac on she went up to 210 and thats normal for these blazers

 

Without the AC it runs a consistant 195, after driving a while with the AC it slowly climbs up, the highest I let it get was a bit over 210 then I shut the AC off because I didn't want to take a chance of messing something else up. This has been happening anytime the outside temp is over 80.

No unusual noises from anything, I haven't tried turning it by hand to check if it is hard to turn, I will check this next chance I get.

 

mine was just doing the same exact thing...turned out to be the clutch fan!!
i would drive about 15-20 min then the temp would slowly climb till i shut off a.c. and temp would go right back down. strange i know...but it fixed the issue.

 

if it stays at 210 its normal with the ac on

 

I have let it go a bit over 210, as I mentioned I would then shut off the AC because I don't want to take the chance of breaking anything else. I could try letting it run a little longer to see if it levels out but it just seemed strange to me for the temp to go up 15-20 degrees just for having the AC on.

hmm, maybe I will try a new clutch, as I mentioned I got a used one to replace mine so that might be bad as well, but seeing as it was still overheating while driving at highway speeds I wasn't thinking the fan was an issue.

 

Ummmmmm, no it isn't. I regularly run with the ac on, and we've been 32C and above here for weeks. Temp is just fine. (Read BELOW 200F) If the ambient air temp goes above 37, that's another story.......



Can you hear the fan kick in at all? Probably more so at idle, and when accelerating from a stop?

Does it overheat without the ac on, and at highway speeds? You could have air in the system. How's you're coolant level; have you noticed any loss? Possible bad thermostat (opening too late/stuck closed) ?!?!?!?

Just throwin' more out there for you to check.


Aaron

 

A couple items to consider:

Didn't see any mention of the radiator cap, check and/or replace.

I know you changed the radiator, so that is clean. what about the wrong fins/per/inch on that new radiator. Not all radiators are built the same.
Not sure how you can check this, specs can be few and far between.

 

Are your hoses weak that they could possibly be collapsing as things get hotter or did you put new hoses on with the radiator. This may sound dumb but try your heater to make sure the anti freeze is circulating through your heater core. Might have a partial clog there restricting flow.