2001 GP Overheating

:dunno: We have a 2001 GP, 3100, with 140,000 miles. According to the temperature gauge the car starts running hot after about 20 miles of driving from a cold start. It will go all the way into the red zone and the dummy light will not come on....it never goes into the overflow or boils. Sometimes it will cool down to about 250....just below the red mark.

Both temperature sensor's have been replaced...the low-coolant sensor and the engine temperature sensor. Before replacing the sensors we could turn off the a/c and the car would cool down to almost normal....215. Since replacing the sensors turning the a/c off seems to have less of an effect on the car cooling down, however, it still does cool it down some. Could the engine coolant sensor be faulty? Is there something that I've missed? Any ideas? :banghead:

Are you losing coolant, have excessive steam from the exhaust, or notice your oil looks cloudy/murky? You could have an intake leak, or a blown head gasket.

With the temperature getting that high are the coolings fans turning on? Check the operation of both fans. Also, unless it has been done I'd replace the thermostat.

This is in reply to both replies......

The head gasket is not blown, not losing coolant, no excessive steam from the exhaust.

We did read the other posts about overheating and had previously checked the fan operation. They are working properly.

The thermostat has been replaced.

Is the a/c relay supposed to go on and off???

Would anyone like to buy a 2001 GP w/high miles?? LOL ;) :rofl:

When the ECT was replaced was that with an OEM/AC Delco or aftermarket? Also, no plumber's tape should be used on the ECT threads because it is self sealing. If it is not overheating then maybe it is just an indicator problem.

The A/C clutch should cycle on/off depending on operating conditions. How well is the A/C cooling? Normally with the A/C on the temperature dips or drops a little.

BTW - When was the last time the cooling system was flushed and new coolant put in?

Check for debris between the radiator and the a/c condenser that may be blocking air flow. Also, did you check coolant level in the radiator or just in the overflow bottle? IF the radiator is full, and there is no debris between, you may have an internally blocked radiator.

The coolant level is full and it's the correct level in the overflow bottle. The radiator was flushed about a year ago so we will try that next.

Did not use any tape. The ECT came from NAPA Auto Parts, not sure if it said Delco or not. :dunno:

The a/c changes somewhat but does not get hot like it would if the car were truly overheating. It actually will get colder when it appears to be running in the red. ?? This seems to be intermittent though. It pretty much does what it wants when it wants. Just when there is a pattern......it changes :banghead:
We also have the same problem that someone else mentioned w/the blower. It blows out the vents on the floor because the switch is stuck in one position...GRRRRRR!!

We have driven this car in over 100 degree outside temperatures over 200 miles at a time and the biggest problem that we noticed was a slight hesitation upon acceleration when it indicated it was running hot. It never boiled, steamed, or anything of the sort when it is turned off after running like this. It's not even filling the water reserve like it would if it were truly hot.

When the sensors were changed there was a significant difference in the way the car acted. Before both sensors were replaced the car would run fine as long as the a/c was off. The new sensors made the indicator run in the red zone. Also prior to replacement, if the car ever did overheat and go into the red zone the dummy light would also come on and a bell would ding. This is not happening now.

There is debris ...mainly bugs....in the lack of a grill in front of the car!! We will also clean that out when we flush.

Was the air purged from the system when the thermostat was changed? If the cat converter is partially plugged, that might be causing heat from the exhaust to affect the temps. If you have an infared thermometer, point it at the therm. housing for a pretty reliable temperature reading. It could also be a collapsing raditator hose, but not likely.
The temperature on mine was up around 210 all the time right before I had to replace the intake gaskets.

NO the air was not purged! How do you purge it? and btw....TY TY TY both VERY much for all of your help so far. :)

NO the air was not purged! How do you purge it? and btw....TY TY TY both VERY much for all of your help so far. :)

On the 3800s we have an air bleeder on the thermostat housing but on the 3.1 there should be an air bleeder valve located on the black tower sitting on top of the water pump (heater line). It is brass. Worth a try. Also, it helps to get the radiator above the engine so park it on an incline. Just make sure engine is up to operating temperature and the thermostat is open. Also, a good idea to turn the heater on before bleeding.

BTW - If you have bad lower intake gaskets on a 3.1L you will know it because you will not get down the road too far. Plus it will boil over and overheating will be very apparent.

If this thing is getting over 250 and not boiling over, then something doesn't seem right to me. Sounds almost like a faulty sensor or gauge. It will definitely start losing power at those temps and usually you can hear the valve train rattling and vibrating. I'd be surprised if the engine has not been compromised. Does it run hot like this every time you drive it or in just certain conditions as in slow traffic?

If you review his prior posts all of that was changed out so very possible the ECT or maybe the thermostat is defective. I don't trust any sensor except AC Delco.

I believe he does have some driveability issue.

He can check ECT sensor calibration with a digital miltimeter. I have the values in some old posts. Same calibration for the 3800 or 3100.

Here is the old post that has the calibration chart. See post #2.

http://www.automotiveforums.com/vbulletin/showthread.php?t=534970&highlight=ect+calibration

It starts running hot like this when we have driven aprox 25 miles....then it will stay that way the entire trip...UGH...

This is the "wife" speaking ....my husband went outside to "let the air out" then we will probably do a test drive. I do most of the driving though and I've noticed that when it runs hotter like that that the engine doesn't want to "go". :( There was a time when it would run hot like that and the a/c would actually get colder....now that is really strange huh?

I'm starting to think after reading these posts that the gauge itself may be off somewhat in addition to whatever else may be going on.

Again ty both for your help and will get back w/u shortly.
Renee

Bob, don't the 3.1's also have an intake gasket problem? Couldn't this be the cause of overheating?

Bob, don't the 3.1's also have an intake gasket problem? Couldn't this be the cause of overheating?

Bingo "W", if we can establish that it is in fact overheating. Affects both the 3.1 and 3.4L GM platforms.

The intake gasket was replaced about a year ago....do you think it could be bad again already :(

If the car is overheating wouldn't it be gurgling, boiling and steaming ....or at least one of those!! It's not doing that. When you turn a car off that's overheating, it's been my experience that it does all of the above.

Hubby is now saying he thinks it is a faulty sensor because it's acting completely different than the other sensor did. ??? EVEN THOUGH it's brand new. He now says it's not a Delco
He replaced the ECT thinking it would make the Low Coolant Temp light go out. This didn't work (obviously). Until he read some other threads from this site he didn't even know the low coolant temp sensor even existed. It works now. The "dummy light" on the dash went out.

Without the a/c running before he changed the ECT it didn't overheat unless it sat in a parking lot for a long time w/the a/c on. As long as we were driving it was fine....and the faster we drove the cooler the car would run.

He did go bleed the cooling system and it's pumping water fine. It shot a stream of anti-freeze out...there was no air in it.

Sounds like you are on the right path. The ECT sensor has a big question mark at this time. Stick with an AC Delco brand because they are better calibrated for the input the Powertrain Control Module (PCM) requires in order to properly display temperature at the gauge and control the cooling fans.

TYVM for all of your help. :) We will let you know the outcome as soon as the temperatures OUTSIDE cools down some from 114 degrees!! My husband will then change the ECT once again.