Thread: Overheating - HELP!

I have a 1999 Grand Prix 4-dr 3.8L. Car runs great.

In the past two weeks, have started having overheating issues. Temp is going up to 215 while driving, then jumps to 225 when idling. Low coolant light flashing, although coolant is full (overfull) in reservoir. Thermostat is original.

When car is overheated, both upper and lower hoses feel equally hot. I opened the bleeder valve. It did take a while for coolant to emerge, but not sure that would have been the issue.

I was scratching my head and then realized that NEITHER OF THE RADIATOR FANS IS COMING ON! Checked both fuses; they are good. Haven't checked relays; don't know ow to do that. But since BOTH fans are not running, it must be something in a common control.

Any ideas of where to start troubleshooting?

I was going to replace thermostat (have a new one), but I don't think that's the issue now.

Any help appreciated.

when you check your coolant level, the overflow doesn't matter, you have to check the radiator, and obviously, don't check it when it's hot. they put the coolant level sensor in the radiator for a reason.

Thanks for all suggestions. It rained cats & dogs today, so I will try everything tomorrow.

One thing I failed to mention and didn't put 2 & 2 together. About the same time the overheating issue started, I noticed that my A/C doesn't blow cold air at all ... Could this be related to the overheating issue ???

Thanks!

Thanks, SgtMarshal: Checked coolant in radiator - it was full.
Thanks, fst. Didn't need to bother with the relays cause I discovered the fans are running but on low speed. (See below)
Thanks, Scottydoggs: Your tip saved me burning my hands!

Here's what I did.
1) With the temp sensor plugged in, A/C on, I drove about 4 miles (30-40 mph) and the temp rose to about 210.
2) Fans were still running at low speed.
3) Unplugged temp sensor and fans went up to high speed. (Temp gauge doesn't dive a reading when temp sensor is unplugged.)
4) When I plugged the temp sensor temp was at 185, but started climbing again.
5) I drove about 4 miles with temp sensor plugged in. Parked and idled for about 2 minutes. Temp was back up to 215.
6) Unplugged temp sensor for about 5 minutes with engine still idling. When I plugged it back in, temp had dropped back to 185.
4) Low coolant was light flashing all the time, whether temp sensor is plugged in or not.

Is it pretty definitively my temp sensor?
Why does the Low coolant light keep flashing. Is this something that needs to be reset?

Finally, with all the plugging/unplugging of the temp sensor, my check engine light has come on. How do I reset it??

Thanks all.

Low coolant sensor is on the passenger side of the radiator about halfway from the top. It could be fouled if you actually have enough coolant. I would get a new one or try removing and cleaning the one you have. I have tried cleaning but ended up getting a used one that worked for cheap.

Following this as I am seeing 210F with a 195 thermostat in 90s outside temps.

So, what I'm reading is that I need a new coolant level sensor AND a new temp sensor. Right?

Thanks, all! Got the coolant temp sensor replaced, and everything is good. My low coolant light is still flashing, but as Scottydoggs suggested, I'll just disconnect it.

My old CTS had been overtightened and was frozen. To get it off, I had to remove the crossover pipe to get better access. That's when I ran into another problem which I have posted on a different thread. (Removing broken manifold crossover pipe studs.)

Thanks!