Two weeks ago, while driving my '02 home, the temp gauge pegged at 260. I hit the A/C a couple times and that brought the temp back to 210. Got home and while idling in the garage, it pegged again. This happened once early last fall, on the freeway. Turning on the A/C cured it that time. Car ran fine on a trip to LA and back a couple weeks ago. Radiator is not blocked with debris.

I displaced all the old coolent with tapwater, then distilled water, then added DexCool for a 50/50 mix. I idled her in the garage a couple times and all seemed just fine, so thought I'd go fill her up at Costco this morning. I was almost there when the temp climbed to 260. I got to the parking lot and raised the hood, with the engine still running and confirmed that the cooling fan was running in 'high mode', but temp remained at 260. I did notice, while driving there, that the temp had steadily risen to about 240, then just went right to 260.

The thermostat housing, lower and upper hoses are all hot, so water is flowing. The system doesn't appear to have air, as I burped it several times and afterward, to more bubbles appeared. While at the Costco parking lot, I even eased off on the resovoir cap a bit to release some pressure, but no air bubbles appeared, just coolent.

Within less than 5 minutes, it was back down to about 230, so I started back home. Within half a mile, it pegged again. I tried turning the A/C on so its fan would help cool, but the A/C wouldn't stay on, so I pulled over and checked everything - again the fan was running on high. I jumped in and made a dash for home. Just before I got home, it went into the reduced power mode (ugly situation - do not try this at home). Got home and shut it off, let it sit for a couple minutes, then re-started and moved into the garage and confirmed, again, that the fan was running, but car wasn't cooling.

What do I need to look into now to cure this situation?

Thanks for any help.

 

Both cooling fans (not cooling fan) were running in high?

Yes -thermostat.
No - check the fans again.

But then, actually driving at about 25mph or faster and it should cool fans or no fans.

Peter

 

Sorry, I forgot to mention that I replaced the thermostat and the fan on driver side is running on high. When I drained the system, it did appear dirty but still had a real orangish color.

 

She has only 50k miles. I changed the thermostat when I changed the coolent. Tomorrow, I'll try the shop manual method for burping the car, I'll also pay attention to see if both fans kick-in.

Thanks.
Dave

 

If air continues to show up in the radiator after you've thoroughly burped it, sniff your overflow tank and see if it smells like exhaust.

Any engine I've ever seen that continually got air in the rad was a blown head gasket.

 

As mentioned already and I wanted to confirm as well, both fans run at the same speed, whenever they are turned on. If one fan is not running, then you need to examine that fan or replace it. FYI, the fan grounds both go through the ground pack at the right forward frame rail adjacent to the hood riser.

 

Ran thru the procedure outlined above this morning. She got to 244 ~ 248 and held for a little over a minute before I shut her off. Both fans were running on high. I let her cool off a bit, then took her around the neighborhood at about 25 mph. She got to 244, again, so I brought her home to rest...

When I get back from vacation, I'll try to find someone with a temp gun to verify the temp.

Thanks for all your help.

Dave

 

Just by chance, hopefully you or someone before you never mixed orange and green coolants?

 

Nope, no mixed coolants.

 

Ive had a similar problem in my GTO. It was a self burping system but there were some bubbles that just didnt want to leave. You really gotta massage those hoses to try to get every bit out. A head gasket can be the culprit. However if it was you would see your coolant needle jump around every time a bubble passed it. That also happened to me with a bad gasket.

 

That sounds like the next logical step. Coolant sensor is very accessible, hopefully that's it.

 

Have you cleaned the fins and spaces on the outside of the radiator, air conditioning condenser, and the space in between the two?

It's routine maintenance on these cars, and is a very common cause of overheating. Don't just go by "it looks OK". Stick a mirror up there, and make sure you have an unobstructed path through both heat exchangers.