Engine Temperature Keeps Getting Lost and Fans Run at Full Speed - SOLVED

[BartAAllen]

Thanks so much for your elaborate reply. The simple conclusion is that GM decided to make the temp. gauge go to zero because of an issue with the thermostat. This fail safe mode is what I never saw clearly explained. They surely can do this though I don't know why they would. Surely the temp. gauge could continue to read the real coolant temperature, but they chose not to. That would likely make most people think that the temp. sensor is the issue. I totally understand now and will be replacing my thermostat using an original GM part. THANKS SO MUCH FOR YOUR HELP!!!

 

[Fless]

Thanks so much for your elaborate reply. The simple conclusion is that GM decided to make the temp. gauge go to zero because of an issue with the thermostat. This fail safe mode is what I never saw clearly explained. They surely can do this though I don't know why they would. Surely the temp. gauge could continue to read the real coolant temperature, but they chose not to. That would likely make most people think that the temp. sensor is the issue. I totally understand now and will be replacing my thermostat using an original GM part. THANKS SO MUCH FOR YOUR HELP!!!

Come back after your thermostat change and let us know how/if it worked for you.

 

[Mistico3]

So I believe I finally found what the issue was. The problem was with the Thermostat and replacing it has finally made this issue go away. The engine light did come one a couple times and the scanner showed a thermostat error and that finally made me decide to replace it.
The main take away here is that one thing I had noticed but did not think was a hint on the problem, was that the Engine temperature would never reach normal operation of 210 Degrees. I thought that this was due to the weather being cold so I did not think much of it. The temperature would only get to around 180 and stay there. However, after 20 minutes of the engine being on, the gauge would simply appear to stop working and the needle would drop all the way to the left and the fans would spin up to full speed. Then, the next day, after getting on the freeway and getting the RPMs in the 4,000 for a few seconds, the temperature gauge would start working again and the fans would stop going full speed but the temperature would still never go above 180 degrees. At any rate, after replacing the Thermostat, the temperature now reaches the 210 degrees, which is right in the middle of the gauge and normal operating temperature and the problem has not returned. Looks like if the engine does not reach normal operating temperature within 20 minutes, the computer senses there is something wrong with the Thermostat or the sensor so it causes the temperature reading to drop and the fans to spin to full speed in case the engine were to overheat since the temperature is not reading normal. This threw me off for months because I was sure it was not a problem with a cable shorting out or with the sensor itself since I had replaced it already.
TLDR; If things seem whacky with the radiator fans and they start going full speed and the engine temperature appears to be broken and not ready any temperature at all sometimes, and other times appear to be working normal, replace the temperature probe first, and if that does not fix it, replace the thermostat. The computer is the one causing these weird things because it is trying to bring attention to the fact that one of those two things is no longer functioning correctly.

 

[Fless]

So all the posters who said "thermostat" were right! Great forum.

 

[MadMax_MFP]

Mine just did the same thing, low heat from the heater and not reaching full running temperature. Replaced the t-stat and working correctly now.

 

[Doubeleive]

So I believe I finally found what the issue was. The problem was with the Thermostat and replacing it has finally made this issue go away. The engine light did come one a couple times and the scanner showed a thermostat error and that finally made me decide to replace it.
The main take away here is that one thing I had noticed but did not think was a hint on the problem, was that the Engine temperature would never reach normal operation of 210 Degrees. I thought that this was due to the weather being cold so I did not think much of it. The temperature would only get to around 180 and stay there. However, after 20 minutes of the engine being on, the gauge would simply appear to stop working and the needle would drop all the way to the left and the fans would spin up to full speed. Then, the next day, after getting on the freeway and getting the RPMs in the 4,000 for a few seconds, the temperature gauge would start working again and the fans would stop going full speed but the temperature would still never go above 180 degrees. At any rate, after replacing the Thermostat, the temperature now reaches the 210 degrees, which is right in the middle of the gauge and normal operating temperature and the problem has not returned. Looks like if the engine does not reach normal operating temperature within 20 minutes, the computer senses there is something wrong with the Thermostat or the sensor so it causes the temperature reading to drop and the fans to spin to full speed in case the engine were to overheat since the temperature is not reading normal. This threw me off for months because I was sure it was not a problem with a cable shorting out or with the sensor itself since I had replaced it already.
TLDR; If things seem whacky with the radiator fans and they start going full speed and the engine temperature appears to be broken and not ready any temperature at all sometimes, and other times appear to be working normal, replace the temperature probe first, and if that does not fix it, replace the thermostat. The computer is the one causing these weird things because it is trying to bring attention to the fact that one of those two things is no longer functioning correctly.

the older trucks would operate normally with low temps until eventually it would throw a code, but the fans would continue to run normal as well as the gauge.
seems to go along with the shutters they put on the newer trucks, it self-checks the shutters if it does get a correct reading it throws a code. so you can't circumvent the shutters, I had mine turned off with a tune it gets hot enough around here already, no shutters needed.

 

[the 18th letter]

I think I’m next on stage to replace the thermostat. Fans running full speed and the temperature gauge isn’t moving. This happened once or twice about a year ago and also noticed my temp only hits 210 in stop and go on a hot day, when it has been working. I think I already ordered the parts. Fingers crossed.

 

[Bagherra]

I went thru this fiasco couple months ago...replaced sensor twice, worked great for couple days then problems would come back. Everyone here said replace tjermostat with GENIUNE AC Delco thermostat. I did and no problem every since....

However, i noticed that before everything started my coolant gauge would normally read around 180......now it gets to 210 and doesnt move at all. Is this normal?

Also, what do yall recommend for a good bi-directional scanner? I currently have a HF that reads DTC's and some live data. Would really like one that tells me coolant temp.

TIA