Thermostat Not Closing All the Way?

[2006Tahoe2WD]

The other day I drove over Sonora Pass CA. On many of the downhill sections I noticed the water temp. dropping a considerable amount (to the quarter point, 150F?). It was not very cold outside (50F). I don't recall any issues in the past with the cooling system able to keep the engine at a constant temp. Anyone else have this happen? Could be time to change out the thermostat?

 

[OR VietVet]

I would not worry about it. Cooler 50 degree air on an engine that is not pulling can cool an engine down considerably. I am assuming, since you did not say, that the temp gauge looked normal when back on level ground and just maintaining speed? When you were pulling up the hills/passes, where was the temp gauge?

 

[2006Tahoe2WD]

Pulling up the hills and all other situations the temp. is steady where it always is. I expect the thermostat to keep the temp the same in all situations except maybe at the very extremes.

 

[Geotrash]

The other day I drove over Sonora Pass CA. On many of the downhill sections I noticed the water temp. dropping a considerable amount (to the quarter point, 150F?). It was not very cold outside (50F). I don't recall any issues in the past with the cooling system able to keep the engine at a constant temp. Anyone else have this happen? Could be time to change out the thermostat?

Yes, this is a common failure mode for thermostats. I had an isuzu rodeo that started doing this and not long afterward the thermostat stuck shut and it started to overheat. I caught it before it got too hot, thankfully.

I agree with @OR VietVet that it’s not an issue as long as it’s sticking open and not closed. But if it changes it’s mind…

 

[OR VietVet]

IMO, I treat thermostats like cooling system hoses. They are maintenance items, not repair items. I would change every 5 years unless there are any concerns like yours.

 

[2006Tahoe2WD]

IMO, I treat thermostats like cooling system hoses. They are maintenance items, not repair items. I would change every 5 years unless there are any concerns like yours.

Not a bad idea.

 

[NickTransmissions]

The other day I drove over Sonora Pass CA. On many of the downhill sections I noticed the water temp. dropping a considerable amount (to the quarter point, 150F?). It was not very cold outside (50F). I don't recall any issues in the past with the cooling system able to keep the engine at a constant temp. Anyone else have this happen? Could be time to change out the thermostat?

Perfectly normal, especially at elevation where temps are cooler like Sonora Pass (9500+ feet). My 03 Tahoe behaves the same way on downgrades. Won’t hurt a thing as it comes right back to normal op temp once I’m back level or start climbing again.

That said, preventative maintenance is never a bad idea.

 

[Foggy]

Not sure what year/info model you drive, but the factory temp gauge is really
just a "suggestion".... It's so far off that I rarely even look at it.
I read it thru my scan tool or my diablosport monitor.. you wouldn't believe how far
off it really is

 

[Charlie207]

Not sure what year/info model you drive, but the factory temp gauge is really
just a "suggestion".... It's so far off that I rarely even look at it.
I read it thru my scan tool or my diablosport monitor.. you wouldn't believe how far
off it really is

Comparing my dash gauge and the actual temp via Torque Pro, I see that my dash gauge doesn't even start to move until the coolant temp is approaching 140-150*.