Ever since it has gotten hotter and I've started using the AC more especially while driving interstate, I noticed the temp gauge on my 2001 Blazer, which normally runs at 190F, has gone up to between 220-230 but when I turn the AC off the temperature goes back down. The outside of the radiator is clean with very little bugs on it so I know that is not the problem. The guy at the dealership thought it might be a clogged heater core or a stick thermostat. I don't know when the cooling system was last flushed as I just bought it in August 06 but I do know that the heater core is brand new (August 06 as well) so I'm not sure if it was flushed when that was done or not. Any idea as to what is causing this before I take it in?

 

How hot is it outside when this happens...? The A/C puts a ton of heat out in front of the radiator. If its hot outside and the A/C is working overtime, this can happen. 220-230F isn't all that bad. A bit high, but for the conditions doesn't sound too out there.

If it weren't going down after you turn the A/C off, then there would be a problem. I think you've found the limit of the stock cooling system.

I guess it is possible that your fan clutch has started to loose its lock-up capability.

 

How hot is it outside when this happens...? The A/C puts a ton of heat out in front of the radiator. If its hot outside and the A/C is working overtime, this can happen. 220-230F isn't all that bad. A bit high, but for the conditions doesn't sound too out there.

If it weren't going down after you turn the A/C off, then there would be a problem. I think you've found the limit of the stock cooling system.

I guess it is possible that your fan clutch has started to loose its lock-up capability.

 

I think the days it did this (at least those that I noticed) it was probably close to 90 outside. My parents have owned a Blazer close to my year (or a Bravada, basically same thing) and I don't remember them having this problem though, hence my concern. In regards to the AC working to keep up, I honestly don't run it that cold. I think the fan was probably on 1 or 2 and the thermostat was set probably a quarter of the way up.

 

Does it do this even when you're cruisin' down the interstate at +60mph? At that point, the natural airflow through the radiator should be sufficient to cool the engine and a/c. If the temps drop while at speed, then you mostlikely are experiencing a failing fan clutch.

 

Yes it does, in fact that was the first time I noticed it. I don't driven enough around town to use the AC much so it typically only gets used for traveling on interstate in the range of 70-80mph. So far I've noticed it takes about 30-45 minutes or so of interstate driving before the temperatures pushes past 210 and then continues to climb. I've only let it go up to about 225F before I've pulled off the interstate and let it cool off. What I've noticed a couple of times once I've pulled off is that it sounds really loud, kind of like it does when it first starts up and start driving until you hit about 2k RPM and it will do this for a little while before going back to sounding like normal.

 

I took it to the shop yesterday and they noticed the gasket around my t-stat was leaking. I had them replace the gasket, t-stat ($11 bucks and change for the new one since I'm pretty sure the old one was six years old so I figured why not) and then also flush the coolant. I haven't had a chance to run it very much yet but it is possible that the leaking gasket was causing the temperature increase due the extra pressure with the AC. I'll have to see what it does this weekend when I get a chance to run it farther than the store and work.

 

My 1999 was having heat problem and gauge was closing in on the red line. I had already replaced the thermostat so I thought it was something else. After replacing the intake manifold gasket because of the 'standard S10 leak' there, the engine was still running hot. I ended up replacing the 'new' thermostat and now I am back at the 195 figure. I guess this means that we can not always rely on getting a quality replacement part.

By the way, I'm here in Calif with temps in the 90's and my temp stays at 195 now. Unless it is REALLY hot, or you are going up hill, your temp should stay around the 195 mark.

 

Got same problem except engine idles rough until ac is turn off then smooth out

 

The replacement of the tstat never really fixed the problem. Taking the cheap route out I decided just to ignore it for a while and put the windows down and the heater on high to bring the temp back down to normal when it was running hot. Since I don't really drive that far it hasn't been a big problem. Today though with a high near 100 going down interstate, it downshifted to up a hill and next thing I know the temp gauge is at 235 or a few degrees higher and I've decided enough is enough. Going to take it back to the shop and let them have another go at it. I had a friend in IL who had a similar problem for a while. Turns out it was her water pump, think that could be my problem as well? I noticed the temp goes up pretty quickly when the RPMs are high, which makes perfect sense but I would say 235 is a bit extreme when that is 40 over the normal.

Thoughts about the water pump idea, could it be or could it be something else like the heater core (even though it was replaced a year ago...stupid thing went out the night I bought it...I was pissed...but that is a different story)?