Thread: '98 Grand Prix GT temperature issues :-/

Ok, so last May I bought a '98 Grand Prix GT. I'm gonna guess it has around 160,000 miles on it but there's no way to tell for sure since the odometer was broke when I bought it. It was not having temperature issues when I bought it but a few weeks after I got it it started getting halfway between halfway and red. At this point I added water because the radiator was a little low but no big deal. That fixed the problem and I didn't worry about it after that. Well a couple weeks later I was mindlessly driving to work and when I arrived I got out of the car and smelled smoke. I opened the hood and there was some smoke pouring out of the engine. This scared me a little bit but I added water and it was almost completely empty. After that I looked for a leak but there but it seemed to hold liquids except for when driven without proper fluid ratios. So I went to an auto parts store and got some straight coolant and flushed the radiator and then added the straight coolant and then filled it up the rest of the way with water and bled the lines. Also at this point I figured it would be wise to replace the thermostat since I had overheated it previously. As it turns out there was no thermostat on there but I went ahead and put a new fail-safe thermo on. After that things started getting screwy... the car still seemed to be getting above halfway on the temperature gauge and the radiator fans would not come on unless the A/C was on (even if the temperature was higher then 230F) I tried replace the CTS but that caused the temperature gauge to dramatically jump all the way in the red even when the car was just started cold. I took it back telling them it was defective and put a different brand CTS on there. This CTS seems to read fairly accurately (usually around halfway) but occasionally it will jump in temperature and then go back down unexplainably. The radiator cooling fans no longer come on when you turn the A/C on and won't come on at any temperature. If I unplug the CTS the fans will both come on at full power so I know it has nothing to do with the fan motors/relays. Anyone have any ideas on what it could be?

CTS is a dual sender.

one signal for your dash gauge and one for the PCM.

The second signal for the PCM is what determines when to turn on your fans.

I am not implying it is still the CTS (ECT), due to the fact that I am unaware of the meaning of no fans even with A/C on.

Cooling system is a closed system.

It should never be losing fluid.

If you are, you have a leak.

Most common is the lower intake manifold gasket, coolant elbows and the bore for the EGR in the upper intake manifold.

All three can and do fail quite often on these motors.

I was working of the assumption that since I originally added water without adding coolant that it some of the fluid was evaporating off because of the higher temperature without the fans being engaged. Also I live in Houston so it is hot ALL the stinking time. I do not know if that is a good enough explanation for the loss of liquids but I could not find any visible leaks.

As far as the fans go, any ideas on what to try? Is it worth trying another CTS? I've already tried two new ones of separate brands, and obviously if the original were working properly I wouldn't have replaced it at all...

I would then suggest a coolant pressure test to ensure there are no leaks in the system.

If the issue is evaporation, the next test is a coolant strength tester. Ensure it is roughly 50/50.

For the fans, it would be most helpful if you had access to a scanner that would confirm that your CTS is reading the same on both ends.