Thread: 02' GP GT Temp Light, but gauge not hot!

Hey all! This is my first post, but I've been reading on here for years to fix my problems!

02' GP GT 3.8 V6 with 102Kmi. Just today I left my house and went no more than .5 mile and my temp light came on under the temp. gauge. The car began running like crap, probably like limp mode I guess. Had no power, couldn't go very fast etc. It did not generate a CEL. It idled like crap also before I shut it of in my garage.

I felt the upper radiator hose and it felt like the t-stat didn't open up yet. Sure enough after about a minute of sitting and not runnng it did open and the hose felt normal and not like water was trapped in it.

Ive read other posts on here, but couldn't find a direct answer really. I heard that the temp light is for an over heating block? And not necessarily the water temp? Would that mean there are two temp sensors? If so where are they?

Im hoping that it may be a bad temp sensor sending a bad signal to the car? Its good to hope I guess! I know the car didnt get that hot, i only had it out for round trip of 1.5 miles! No visible water leaks anywhere else on the car. Its in great shape and pretty dry! I might add the car sat in my garage for almost 4 weeks without being driven before this happened.

Any thoughs/answers would be appreciated! Thanks!

Sounds like a bad coolant temp sensor. It's located under the thermostat neck and screws into the LIM at an angle. Probably getting a bad reading. I'd change that and see what you get.

What did the temp gauge read when this was happening? Is your coolant full in both the rad. and overflow?

Thanks for the info. Thats what I was leaning towards in other reading I've done since this post last night. Yes, my coolant in the radiator was full as well as proper level in the overflow. The actual gauge in the cabin was reading barely above the lowest reading on the gauge (It may have been 170???).

Something else I read was everyone telling everyone else to get rid of the dex-cool as it's no good! I saw talk of a class action too?? I read this quick, so that part could be wrong, but they were definitely saying get rid of it. Ill check on here to see what others are saying. Any thought on that as well?

I probably should change mine as it's been 75kmi on my dex-cool at least, and I didnt know others were getting rid of it earlier!

Yep, sounds like the temp sensor then. Make sure you put a little teflon tape around it before you re-install it as it may leak. It's not in the easiest spot to get to but can be done. Of course when you pull it you will loose coolant and need to refill/bleed the system.

There may have been a class-action against GM for the Dex. Never really looked. At 75K I would def. flush and refill the cooling system.

Here's my thoughts on Dex. If your cooling system is leak-free and does not have a BIT of air in it and you change it often then Dex is fine and will not cause issues. Where you run into issues (especially on these cars) is when people read the sticker on the pass. strut tower and don't change it until 100K+, or when you develop a coolant leak due to the LIM or elbows and introduce air into the system. When Dex meets air it doesn't like it and turns nasty and will clog everything up from heater cores to rads and attack gaskets. If you take the cap off the rad and have some reddish/brown junk on it then it's time to flush/fill.

I personally went w/ the normal green coolant when I dropped my new motor in. I had a new rad. and heater core go in at the same time so I figured I would avoid that issue altogether. Luckily the used motor I got was well maintained and showed no signs of the Dex going postal in it. Even when I installed the new LIM gaskets it was clean. Flushed it and away I went. Been fine ever since.

Also, don't mix Dex w/ the green stuff. Once again bad things can happen as they don't mix well if at all. It's totally up to you what you want to put back in, but from my point of view I'd rather run green and just change it as it should be and not worry about it eating gaskets or clogging things up just because I got a small leak in a coolant elbow or something. My temps didn't change either so its not running any hotter/cooler than with the Dex.

In the end it comes down to personal preference, your maint. schedule and the condition of your cooling system.

Also, when you go and bleed the system do a search for that here as well as these cars can be a pain to get the air out of completely. I bled mine 3 times before finally getting all the air pockets out. See the brass bleeder screw on top of the thermostat neck? That's what you use. There are other tips on this site as well.

Thanks for the input. I changed the sensor and the car now runs normal with no temp. light on. However, It runs hot now, like above 210, maybe around the 240ish range. I didnt let it get above that so I parked it. I opened up the bleeder on the T-stat housing and let it idle for a bit, but the temp hovered around 225-230ish. Maybe it needs more bleeding like you said? Also I noticed my cooling fan didn't kick on, shouldn't it have? I could've sworn in the past sitting idleing some where hearing it kick on and off. This time I got nothing. What controls that?

I checked fuses quick and banged on some relays etc. Didn't see anything at a quick glance. Guess Ill do some searching on here for that next!

How long would you say the car needs to run/idle etc. with the bleeder open to get all the air out? Would it naturally do it overnight If I left the bleeder open and the rad. cap cracked? Kind of like brake lines sometimes?

Thanks for the help!

A little update : I got out my scanner and turned on/off both cooling fans, so I know I dont have a bad ground etc. I watched the data and noticed that the gauge inside the car reads about 12-14 degrees higher than what the computer says it is. Ex. at 185 which is where the car normally is : the computer would say 172. , is this a normal thing? I know not many people probably compare the two readings, but maybe this is correct and no one ever cares?

So when the computer reached 212 I did watch both fans kick on, so thats good. I guess I got nervous before and shut the car off, as the gauge would've read 225 or so.

I totally flushed out all the old dex and went with an all systems brand green. It's still running abnormally hot (207 computer, 220 or so via gauge) Ive been bleeding the air out, and it doesnt seem like theres more in there. But if the temp isn't right yet, I'm guessing there has to be something in there??

Ill try some more tomorrow and re-post.

The 210 range is about normal. With it reading a bit higher it may still have some air in it somewhere. And yes, leaving the cap off overnight couldn't hurt. When you were bleeding the system did you have your heat set to full hot and fan on full blast? There could be some air trapped in the heater core.

I think someone mentioned jacking up the front end to help with bleeding. I'd turn the heat on full blast, let it idle until you hear the fans kick on and then crack the bleeder and see what you get.

Don't forget to fill the overflow bottle to the hot or cold marks (depending on the temp of the motor). If it's empty I could see it adding air back into the system.

That"s the normal temp range for these engines. Mainly due to the 195F temp rating of the thermostat. It will start to open at that temp rating , but won't fully open till 200 or so.

Thanks guys. Well I think I have a conclusion, so here goes:

The old temp sensor may have been wacked out when I bought the car? I always read that it's temp (by the gauge inside) was at 185. After putting in the new sensor and seeing it ride normally around 210, I thought everything was hotter.

I NEVER hooked up the scanner before with the old temp sensor, So I can only assume that it was reading LOW inside the car, and that the car was really around 200-205 or so. Now with the new unit in the, the scanner still reads that same 200-205 operating temp, but my gauge inside would read about 11-13 degress higher than the PCM!

I thought the new sensor may have been wacky (Advance Auto Parts BWD Part #), so I bought another one (Delphi part #) and installed it. Well, I have the same difference in readings between the PCM and the gauge inside, about a 11-13 degree difference. So now I know it's not the sensor and it's a gauge thing. So I guess normal people just assume the gauge, and if it says 210 in the car, they think it's 210, when really it's 198 or so. I know it seems minor, but I was used to 185, so instead of my gauge reading lower, now it's higher, which from what it sounds is more normal!

I'm not sure If I tried the heater on full and then bleeding it, but Ill give it a shot. After a 30 mile drive last night and monitoring things, I think all the air is gone hopefully.

Now the last question or thought is : Is there a ways to calibrate the temp gauge inside the car with what the actual PCM is reading?? It shore would be nice to know it's the same, for what it's worth!! Anyone looked into this?

Thanks for the advice guys.

It wouldn't surprise me if it was. I read in some other places on here of people explaining the same things. I wonder is you could take you car to advance and see if they can read your coolant temp. with their scanner? That way you'll know for sure and it'll be peace of mind just knowing the needle is off and high.

I know someone mentioned on here about taking the gauge cluster apart when the cars cold and moving the needle for the gauge. And I know there companies that calibrate dash clusters etc. Personally myself I dont care now, I know it reads 11-13 degress high and theres no problem, so I wont be trying either of those solutions! Plus, I hope to not have the car much longer as Im really looking for a GXP!

Good luck.