Engine runs cold replaced the coolant temperature sensor?

Tiny
MIKE1961
  • MEMBER
  • 2012 CHEVROLET EQUINOX
  • 3.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
It has recently become very cold where I live. A month ago, I replaced the coolant temperature sensor in the 3.0 L V-6 VVT engine in my 2012 Equinox because it had failed. At first, it didn't work. But I took off the negative battery cable to reboot everything, and it worked!
About a week and a half ago, it got very cold out. When I drove the car, the temperature guage just barely moved up. The heater barely blew warm air, even after driving for 40 minutes. The faster I drove, and the more I turned the heater fan up, the more the temp guage went down to almost zero. This was new, it has never happened before.
It seemed very obvious that the thermostat was stuck open.I had it replaced, and on that day it was much warmer outside. The temp guage came up and there was hot air from the heater. I assumed the problem was fixed. Not so!
Today it was very cold again. I drove the car for half an hour, and it was doing exactly the same thing!
The controls for the heater all appear to be working properly.
The engine is running cold, even with a new thermostat.
What else could cause this? Is there perhaps an air block in the coolant after the repair? But it is doing exactly the same thing as before the repair!
Thank you in advance for your consideration and knowledge in this matter, Mike1961
Monday, December 22nd, 2025 AT 12:25 AM

3 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,346 POSTS
Is the CEL on? Do you have access to a scan tool that can read live data? From the description it sounds like either the ECT isn't reading correctly or the cooling fans are staying on. However lets look at some things first. Check that the coolant level in the tank is correct. An air bubble in the system could cause this. However if it was working and then stopped it's likely not air unless the coolant is low or leaking. Next start the engine and open the hood and see if the fans by the radiator are on. On a cold engine they shouldn't be, if they are they can keep the engine from warming up. That is also why the faster you drive and the faster the blower turns the colder it gets, the airflow over the radiator cools more and the higher airspeed over the heater core pulls the heat away faster. If the fans on the radiator are on all the time it's possible the coolant temp sensor is faulty or disconnected. If it get's disconnected the PCM looks at other temperature sensors and the engine status and if it's running it turns the fans on because it doesn't know the actual operating temperature and tries to protect the engine from overheating by running the fans.
If they are not running then it's possible the new thermostat has a problem, with the quality of parts these days I suspect every new part of being bad until I test it to see if it works.
Now there is also another item, do you have the manual control head or the version where you dial in a temperature and it does the rest? The automatic versions can have the aspirator plug with dirt, hair and then they lock up. The system then will stop working, but usually this will get you a flashing light on the control head and codes will set.
Check on the fans and coolant level and reply back. I know how it is to drive without heat.
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Monday, December 22nd, 2025 AT 5:11 AM
Tiny
MIKE1961
  • MEMBER
  • 26 POSTS
Hello Steve!
I finally found the time for the Equinox. It's Christmas and it's been frigid. Today was much warmer, only a few degrees below freezing!
I have answers for all of your questions, as well as some interesting observations too.
The Check Engine Light is NOT on. I recently replaced the Coolant Temp Sensor as it had failed. It is working properly now. I raised the hood and checked the coolant level in the reservoir. It was only 1/2" below the cold fill line.I started the engine with the reservoir cap off. The radiator fans were not running. I ran the car in the garage for a full 40 minutes, The fan was on it's lowest setting. The temp guage only came up to 3/8ths, it typically runs at 1/2.
After 40 minutes, the coolant in the reservoir came up to only 1/2" above the cold fill line. There were no coolant air burps, even after I revved up to 2500rpm for about a minute to try to get something to happen. Twice. Not once did the rad fans come on!
The upper rad hose heated up very slowly, and even after 40 minutes I could still hold it in my hand. The lower rad hose did not heat up at all for a full 30 minutes. It never got hot at all, only finally warm.
So! The engine runs cold. There's no air in the coolant. The CTS and radiator and water pump and thermostat are all new. So where is all the heat going? It sounds like the thermostat is stuck open, but there's not a mechanic on this earth who would install a new thermostat that was already stuck open. Am I right?
I am finding this quite frustrating, but also quite fascinating as well! I can't wait to find out what's going on !
Your thoughts, Steve?
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Wednesday, December 24th, 2025 AT 12:04 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,346 POSTS
The new thermostat may not have been stuck open when it was installed. As I said, parts quality has gone far into the toilet even with some OEM parts. I would pull the one in it and test it because what you describe sure sounds like it is open. However I'm surprised you don't have a code P0128 though. You can test it without opening the engine but you need to buy a couple temp sticks (basically controlled melt temperature crayons) A 188 Tempilstick and a 206 Tempilstick. You then put a dab of each on the water outlet housing. Then start the car and drive it around. Then you check them, the thermostat should start to open at 194 degrees and be fully open by 225 degrees. You can also look at the reported temperatures on a cold engine, the ambient air, coolant temp and intake air temp should all be within a couple degrees apart. Then start the engine and watch the coolant temp, if the thermostat is working the engine temperature should go up reasonably fast (within 5 minutes it should be getting close to the low thermostat temp) then you should see it drop as the thermostat opens and lets cold coolant in. Then it should rise again and cycle a few times as it heats up. The upper hose should stay cold until the thermostat opens and then it will get hot and then stay warm until the thermostat opens more and it reaches operating temperature.
The OE unit is part 12651113 from GM.
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Wednesday, December 24th, 2025 AT 4:24 AM

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