Hi all,
I have a 2001 LT 4dr 4wd with a 4.3 auto and this summer it's been running hotter than normal. Basically, if I run the AC and get on the highway, it gets into the 230 degree range. I normally turn off the AC at this point and it brings it back into the just below 210 range.

I've had the cooling system flushed, checked all of the intake related items and I plan to change out the thermostat next, but normally I think of a bad thermostat as behaving differently. I never thought that was the issue. The radiator looks good with no issues.

Anyone have any ideas?

 

Check the fins on both the condensor and the radiator. Poor air flow could cause this.

You said the system was flushed, there may be air in the system.
Was the Dexcool still in there when you had the system flushed? Im thinking the radator may actually be partially plugged with goo. Unfortunately flushing doesnt get the goo out.

You are correct about thermostat behavior. Since you can control the overheating by turning the AC off, Then its not the thermostat.

Good Luck!

 

they actually replaced it with Dexcool, (they never asked me and I never gave them direction otherwise) and yes the old was still in there.

 

mine did this same thing...it was the clutch fan.
fixed it...after checking t-stat and air in system and levels...turned out to be the fan.

 

All the fins are good. Forgot to mention that I replaced the radiator cap. No difference.

After thinking more about this, and knowing how temperamental Dexcool is, Sludge clog makes a lot of sense.

If a flush doesn't get that stuff out, will anything? New radiator?

 

did the fan not turn? Mine does.

 

no the fan turned, it was turning to easily in fact.
i compared it to the new one once it was out and it had little resistance when compared to the new one. i think under load it wasn't getting enough "traction" and not turning fast enough to draw the air flow i needed.
what ever the reason it fixed the issue.

 

If it's overheating going down the hiway with the A/C on then it's most likely not the fan as it has little to no effect since the movement of the car is pushing the air through the radiator. If it was only overheating when stopped at a light then you could look at the fan as a cause. I'd check out the radiator for partial plugging since I've had 2 get gunked up. Regular garden hose flushing did not clear it but I never tried a chemical flush. After the vehicle is warmed up turn of the engine and feel the radiator fins to see if they are cooler towards the bottom which would indicate a lack of hot water flowing through the lower channels.

I also had one time when I couldn't get the air out even burping it using Swartikk's raise the front method. What I wound up doing was putting a submersible utility pump in a 5 gal bucket and pumping coolant into a flushing "T" while running a return line back from the radiator cap to the bucket. Took an old radiator cap and drilled it out for a hose fitting. You have to let it run for a good while as the coolant from the bucket needs to get hot so the thermostat opens up.

If neither of those work then you could be the one person in the world who had a water pump impeller fail without the shaft bushing fail first and leak. Actually I'm sure someone has had an impeller fail...I just haven't seen one myself..at least not on a GM.

 

One more thing I should add, When this happens, if I turn the truck off to run into the grocery store and come back inside of 15 minutes or so, then the temp needle is pegged until I run around for a minute. This can prompt an episode.

 

The radiator is plugged. This happened to me as well. Going down the highway should make the engine run at operating temp even with the a/c on due to air flow over the radiator. When you stop to run in to stores on short trips your radiator still should "radiate" the heat off the coolant aka heat soak. Since you had a flush it is most likely that deposits left behind got stirred up. They are starting to, or have already clogged passages in the radiator. Good luck but in my opinion the only way to resovle this issue is by replacing the radiator. No amount of flushing will fully rid the system of deposits.