My 96 SE has the same problem and I don't have a SC.

YES! The Radiator Cap!!! My "spare" car is a 1984 Toyota Corolla and many moons ago I had a similar problem. I interogated the usual suspects except, of course, the obvious. Once I replaced the Radiator Cap with a new one, my cooling problems were over. In my case, I believe the cap wasn't allowing any pressure to build up and somehow this helps keep the temperature down. I'll be changing the WaterPump, Hoses and Coolant in my Olds soon. And for an extra few bucks, I'll be changing the Cap too.

I hope this simple suggestion works for you too.

Do you have the service manuals? I might suspect that although your car is heating up, it is not heating up as drastically as you might think.

Try monitoring engine temps using the climate control display, and see where you are really at.

There aren't many hills around here, so I couldn't tell you if I have had a similar experience.

from my experiance, i think it has something to do with the supercharger, because if you've ever felt how hot it can get, it would make sense.
one day i was out with mom and i was driving her car, a '97 cavaleir, and i had the engine running for close to 2-3 hours and while she was in the bank for a half an hour i left the thing running with the a/c on and it stayed at a constant 195 degrees....
i only wish i had a car that i could leave idle forever and it would never get hot

that brings me to another question, yesterday i saw a big ford deisel parked out in the best buys parking lot, and there was a lady sitting in it, and it had to have been idleing for over a half hour to an hour, how the hell does that work, and why do people with deisels always leave them running for extended periods of time?

If the radiator caps are both defective, then there should be a lof of GM vehicles (with and without superchargers) that have the same engine heat problem, right?

My 97 SSEi and 92 SSE both overheat if in traffic with the AC off so its not just a */C thing.

If the AC is on, they never overheat, even in traffic or under load in the hills.

On the highway they never overheat, even with the AC off.

Seems like these cars have a cooling issue. Just keep those fans going and you should be ok. Once that engine starts getting real hot, the thermostat wont really matter as it will be wide open all the time.

I have heard of some SuperStant Thermostats not opening fully due to the size of the pellet hitting the inside of the engine block. Maybe something for you to check. I have 180 SuperStants in both of mine and they work fine.

The RED Zone does not sound anywhere near normal. I have heard that sometimes the fans wont come on until the temp gets around 240 or so. There are some kits out there to make the fans come on faster or all the time.

Cheers,

Andrew

Caps go bad just like anything else - it'* rec. you replace them every flush. If the gasket is good, not dried/cracked or swolen, you can usually use them a while, but they can casue trouble sometimes if they leak and I usually end up replacing mine every 3 years or so.

The most obvious things have been listed here - it is possible you may have the wrong part installed, or one that'* new but failed, too. Have you checked to make sure you are getting fluid flow? With the engine cold, remove the cap and start the engine. As it warms up and the tstat opens you should notice the fluid get warm and start to circulate. Once it gets hot the fluid will start to come out the neck. Turn it off and put the cap back on. That will give you an indication if the tstat and pump are working. If so, I'd take it a radiator shop and have them check it out because it'* definitiely not something to ignore.

btw - how many miles are on the cars?

There'* 140k miles on the '93, and I don't know if the engine has ever been rebuilt. It doesn't burn oil, and runs great.
There'* 150k on the '92, and the engine was rebuilt at 100k.
I bought both of them in 1999.
The radiator cap gasket looks ok and the gasket doesn't leak coolant.

If the tstat weren't opening, it certainly would have overheated in daily driving shortly after I replaced it. And yes, when filling the radiator I run the engine with the radiator cap off and slowly fill until shortly after the tstat opens and sucks more coolant into the top of the engine.

I took a peek at the ClubGP web site posts and saw complaints about heat in the Grand Prix too, and they talk about wiring kits to trun the fans on whenever you want, and also a larger radiator that you can buy.

I hope someone can help identify the cause of the problem...I asked a certified GM mechanic about the engine temp when it first happened on my '92, and he said it sounded normal to him, nothing to worry about, these engines can and do operate at 240 degrees F and won't suffer damage...but being that close to the RED zone makes me really uncomfortable, especially with my wife and kids in the car.