Changed thermostat, Coolant temperature stays at 185 degrees

[SpaceBaller01]

So I've replaced the Thermostat (after noticing that the coolant reading no longer goes higher than 185 degrees. The new one is a GM, should be stock 185 degrees. However my coolant temperature doesn't go any higher than 185 degrees still. Intermittently getting a CEL for too low coolant temperature, if reset it'll go away for a while but comes back eventually. It doesn't seem to matter how long my trips are, goes no higher than 185 degrees. It is affecting the heat as well, am getting heat but not as hot as I would expect (like setting to 84 gets 74 degree level).

 

[B-train]

If you put in a thermostat that says 185 (the temp is stamped on the bottom side) that's all you will get. 185 is its opening and modulating temp.

If it's anything newer in the GM line, I'm pretty sure they all come with 190F (some say 187F) t-stats from the factory. I don't think you have a wrong temp from what I can tell.

I'm speculating you might have 1 or 3 different issues providing what you put in was OE equivalent.
1) defective new part that is bypassing and not sealing fully.
2) installed incorrectly allowing coolant to bypass thermostat while under pressure from the water pump. (Generally speaking this is hard to do with the newer stuff with o-ring type seals. They only fit one way correctly). Is it in the water housing with the spring side submerged and the pointed side facing the upper hose to the radiator?
3) air in the system after replacement and needs to be burped. Take cap off while cold, run to operating temp, let circulate for 5 min at temp, shut down and heat soak, top off as needed. Retest afterwards. You'll know if it's full of air or not depending on how much the level drops with the cap off and t-stat cycling.

You can also double check correct operation with an infra-red heat gun. See what the t-stat housing temp is when warmed up. You can also check the upper and lower hose temp delta to see how much heat is / isn't getting rejected through the radiator.

 

[B-train]

Correction, depending on the year of your vehicle they could have used a 195F as well. I do know that there are different temp options for performance or industrial applications of the same engine.

I'd double check to make sure what the OEM one you removed has stamped on it, or check with a dealership parts dept to see if they can give you the exact spec from new.

 

[Fless]

When this "too cool" problem started, what work had been done just prior? Any chance you're running an aftermarket radiator?

Read this: https://www.tahoeyukonforum.com/threads/cold-case-radiator.135572/post-1699853

You could try pinching the small return line that goes from the radiator to the surge tank to see if that makes any difference.

 

[OR VietVet]

The stock thermostat for your rig is 195 degrees. That makes a difference for your heater and for the open and closed loop for the emissions. Put the correct thermostat in there.

 

[Fless]

The stock thermostat for your rig is 195 degrees. That makes a difference for your heater and for the open and closed loop for the emissions. Put the correct thermostat in there.

Curious, where do you see that? RA shows OE for the 2004 Yukon XL 5.3 (listed in the 1st post) to be 187°F.

 

[swathdiver]

The stock thermostat begins to open at 187 and is fully open by 195.

 

[OR VietVet]

My 05 calls for 195 degrees and I ASSUMED that the 2004 did too.

 

[MassHoe04]

If the weather where you are is already cool, a thermostat stuck open could explain your heat feeling cooler than normal.

Is it possible the thermostat is stuck open or backwards?
Is that possible on the GM stats @OR VietVet?

I know I saw some people on Wrangler forum did not pay attention to how the original stat was positioned in their 4.0L and ended up putting the new one in backwards. But I forget what the exact implications of that reversal was. I am not sure, but I think they started off cold, then overheated after the stat opened (which was closed because it was in backwards...).

 

[THarber]

Did you change the settings in the ECM to make fans come on sooner? If not, it will always run the same temp.