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Overheating - HELP!

J

jammy

New member
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.
 
see if you can replace the fan relay(s) or swap them with a similar relay that you know works (one that isn't in use when you're testing the fans to come on at operating temp obviously). if the relay isn't the issue then bust out the multi-meter and check if there's power going to the fans.
 
Considering your car is over 18 years old, your fan assembly might have just died. It happened with my 2000 GTP.
 
your ac work? if so turn it on, both fans turn on?

if they do your temp sensor is bad. unplug it and the fans should both turn on full time. this way you can still get around with out overheating.

if the ac dont work, you can just unplug the temp sensor. both fans should then work. (if the temp sensor is bad)

little tip. if you follow the pig tail it leads to a plug up near the dog bone on the lim, unplug it there, cause the temp sensor is near the exhaust. hot hot hot.
 
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.
 
i break 210 all the time when its hot out. i run a 195 t stat as well.

the coolant sensor, take the pass headlight out, then reach in to the side of the rad and unplug that pos, never look back at it, bye bye light.

id say your temp sensor is bad. now heres more bad news, these damn sensors are more times then not, bad new in the box, could take a couple of new ones to get you right again, just a warning, dont just trust the new one right off the bat. brand dont seem to matter, they all can be bad new in the box.

if you got a local junk yard you might have better luck with a used one. hell mines got 240,000 miles on it, i took it from my old engine and installed it in the new one, cause i know this one works.
 
coolant level sensor is 100% optional in my opinion, mines unplugged for like 4 years now. i do check my fluids now and then. as we all should.
 


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!
 
damn thats why you pulled them bolts off. wish you had asked, we'd have told ya to not take them bolts a part, cause they usually break on ya. when we do remove them its cause headers are going in, so we dont care if they snap or not. its best if they do snap tho, big time saver lol

open end wrench worked well for me in the past. even a large adjustable should have got it done. that dog bone mount is only 3 easy bolts as well. that could have opened up the area some as well.
 
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