Possible faulty thermostat

Tiny
JEFF HERMAN
  • MEMBER
  • 1998 CHEVROLET BLAZER
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 237,000 MILES
First of all the owners manual says 1998 but the door jamb sticker says 9 of 1999. Anyways, the temperature gauge on the dash only reaches about a hundred and twenty degrees which is actually accurate to the infrared reading I took off the engine after running it 20 minutes. I tested the thermostat in boiling water and it seemed to be closed and then open up when the water got hot whether it was exactly a hundred 85 degrees when it opened I don't know but it did appear to open. I cannot see coolant circulating in the radiator when the cap is off and the engine is warm. Several questions could I still have a faulty thermostat? Could I have a faulty water pump. Third could I have a clogged radiator? If you have other suggestions I'm all ears. Thank you for your assistance as always.
Thursday, February 18th, 2021 AT 9:13 PM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Does the vehicle actually overheat or have any cooling issues? If you put the thermostat in a pot of boiling water it should be clearly opening. So if you are not sure if it opened then it is faulty.

https://youtu.be/5w14DkYn1bU

https://www.2carpros.com/articles/how-an-engine-thermostat-works

As for not seeing the coolant moving, that is not uncommon. Clearly it does sound that the temp is too low but the temp sensor is on the engine side so if it is not opening and flowing the coolant then you would see the engine side coolant getting hot and it would overheat.

So it sounds like the cooling system is operating and keeping the engine cool. If it overheats then we are in a different camp. Thanks
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Friday, February 19th, 2021 AT 3:42 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
The engine is not overheating. The engine won't rise above 150 to 160 degrees after driving it. This is below the normal operating temperature. The radiator seems to be very clean inside I just flushed it and change the coolant. When I start the truck and it's cold the fan is even running back to me doesn't seem right could I be having a problem with the fan running too much.
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Friday, February 19th, 2021 AT 4:04 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. I understand now. Just to confirm the fan runs all the time? If this is the case, your fan clutch is stuck and causes the fan to run when the engine runs and this is not going to allow your coolant to come up to temperature.

https://www.2carpros.com/articles/fan-clutch-symptoms

https://www.2carpros.com/articles/fan-clutch-removal

Below is some more info on this but it sounds like it needs to be replaced.

Let me know if I am still missing something. Thanks
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Saturday, February 20th, 2021 AT 5:31 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
Put in a new thermostat and continue to bleed air out of the system and fill with coolant and it appears to be running properly now. Not sure the exact motor temperature but the dash gauge was a couple marks below 210. Plenty heat in the car now. Thanks for your help.
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Saturday, February 20th, 2021 AT 6:12 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
That is great. Must not have been closing because that is the only thing I can thing that would cause this.

Thanks again for using 2CarPros.
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Sunday, February 21st, 2021 AT 6:50 PM

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