Bizarre temperature behaviour-94 GP 3100

[green_souljah]

Hey guys

This problem has stumped a lot of people so if u have any possible idea of what the problem may be, I am all ears.

It's my girlfriends 1994 Pontiac Grand Prix, 3100 V6.
The temperature guage will shoot up to almost danger levels, when it is
COLD...like Im talking -25, -30 degrees. When this happens, the heater stops blowing warm air.
To send the guage flying back down to "normal" readings, all you have to do is rev the car to 2000 RPM and you can watch the guage drop.

It does not do this in the summer, which is the time of year one is concerned with overheating causing damage.

Now I know that there is no way the car is actually overheating in these frigid conditions, what could it possibly be?

I replaced the thermostat, no change
Coolant is always up
Now, our local dealer suggested it could be an intake seal problem, which I highly doubt.

Anybody?

I am stumped.
My girlfriend has a twenty minute commute, and her car is cold for the majority of it.

Did I mention we live in Canada?




Thanks in advance!

[robby1870]

My temp gauge went crazy like that when the cluster went stupid. I had to re-solder the cluster. Also, when you changed the T-stat did you bleed the system?

[green_souljah]

what do u mean by cluster?

Yup I bled the system, I do it every time I change the oil

[SappySE107]

The gauge cluster. The only time my car would heat up like that was when the head gasket blew between the coolant passage and the cylinder. It would increase the pressure a lot and throw coolant out of the block and into the overflow. I had to run it at 3000 RPM to keep the temp down, since it would cause the coolant level to rise in the block. Just to be safe, I would go to autozone and rent the coolant system pressure checker. That will tell you if you have an internal leak like I had.

If its not that, it could just be the sensor, but the RPM thing doesn't really have much to do with that either. There should still be 2 sensors, 1 for the computer and 1 for the gauge. The 1 for the gauge is based on the rear head I believe (never owned a 3100, just a 3.1). If the coolant level is low, that would put less coolant in the rear head, and cause it to heat up till the RPM goes up and the pressure increases, making the coolant expand. Im rambling, ok, I think coolant level is low, for some reason.

[green_souljah]

Well, Ben you have made the most sense out of anyone I have talked to about this.

The reason I dont "think" it's the head gasket is the car runs fine, other than this, it goes through a small amount of coolant, like maybe a quart a month? Not enough to worry about anyhow, and the oil is free of any coolant contamination, no sweet smelling exhaust either. Now, I am not 100% confident in my answers because I have never owned 3100 before, so if there are any points I am overlooking here...

While the guage says its close to overheating, I really don't think that it is.

You wouldnt happen to know the name of these two sensors would you?

Thanks a million, at least I have somewhere to start now.

[robby1870]

one is called the CTS (coolant temperature sensor) and I think the other one is called that too. I think the rear head is the one the gauge uses, like Ben said. Ive changed the one on the rear head before, very easy. My gauge would shoot to 260 at start up and then come down, then hit 260 again, then 100, it was all over the place. Changed the sensor, problem solved

[SappySE107]

My car ran perfect, the only reason I knew something was wrong was because the temp would get up to 210 at first, then down to 195, then 215, 195, 220, 195, 235. I had to run it at 3500 on the way home once because of it, and it kept cool. I had no coolant in the oil, just coolant loss that I couldn't trace, and the overflow was always full/overflowing. After the engine cooled, the level would go back down in the overflow.

They are both called CTS, but have different connectors.

[Jake]

The 3100 in my 1995 Pontiac Grand Am GT had similar problems only in winter and it was traced to air in the cooling system. Once the system was burped it registered normal temps.