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.

 

[OR VietVet]

I would have to dig for info but I think the thermostat housing will not fit if the thermostat is in backwards. Besides, what kind of numbskull would install it backwards?

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...).

 

[MassHoe04]

I would have to dig for info but I think the thermostat housing will not fit if the thermostat is in backwards. Besides, what kind of numbskull would install it backwards?

OK. Thanks. I had no idea if even possible on GM. Was just a question/thought, after recalling some of the stuff I saw posted when I had my Rubicon.

The thermostat housing on the Jeep allowed the possibility for the stat to be put in backwards. The casting has enough room for the longer plunger side to clear if it were facing the front instead of the block as it should... It comes up a few times on the Wrangler forums.

 

[OR VietVet]

Cooling systems are very important. Next to the oiling system, the cooling system controls that engine heat. If you work on your own rig/engine and install the thermostat backwards, I hate to say it but you deserve any negative effects that you created. Like I have said a few times on here, When I ran shops I had a couple customers tell me oil changes are easy and I said, "Yes, if they are done right".

@MassHoe04, I knew you were not talking about yourself but i get a cringe when important systems are looked at as "simple" by some people that "think" they know what they are doing on their rigs. I am alll about saving some money during maintenance and repairs on your own rig but for criminy sakes, do your rig right and treat it like the great engineered and designed vehicle that it is. Give it a chance and it will treat you right.

 

[MassHoe04]

I found out that the backing plates, brake shoes and parking brakes can be installed on a Model A Ford axle on the wrong sides and upside down one time... I wondered why the brake rods would not reach actuator arms at the far back side. But I was 10 and we didn't have internet, Google or YouTube!

 

[Fless]

I found out that the backing plates, brake shoes and parking brakes can be installed on a Model A Ford axle on the wrong sides and upside down one time... I wondered why the brake rods would not reach actuator arms at the far back side. But I was 10 and we didn't have internet, Google or YouTube!

Coulda called someone on the rotary phone... BR-549?

 

[Donal]

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).

OP has not responded to any replys, so far. Need to confirm fan clutch or not.

I have run 160F thermo in 2005 Z71, completely stock engine, and never got a "low temp CEL." I have run 195F as well. I have had a 180F in for the last two years. I have replaced the temperature sending unit located below the alternator two years ago. Operation with all thermostats has been consistent. Dash gauge shows correct and verified temperatues with temp gun. Original fans and configrations.

Dash gauge shows thermostat temperature (180) during hiway speed of 68 mph and higher operation from start up to first stop. First stop may be in two hours or 30 minutes. Gauge then shows norrmal operating temperature of 195-210 during stop and go or hiway operation. AC on, ambient temperature has no affect.

If I was OP, i would replace the sending unit and conifrm the temperature.

The thermostat only guantees the low temperature and the operating temperature is most always higher than thermostat rating.

 

[MassHoe04]

OP showed 2004 in signature.
Original would be clutch, but he has not responded with information on whether he has OE stock or E-fans transplanted from another truck.

 

[OR VietVet]

Crickets are a PITA.

 

[Z15]

AC Delco lists only one part for this model year and the opening temp is 187°.

 

[SpaceBaller01]

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.

Yeah I'd be pretty surprised if I installed this incorrectly. The unit ought to be facing inward towards the engine, same as it came out.
Now for burping the system I ran it a good while after I replaced the thermostat. And it dropped down quite a bit, I checked for a few days afterwards and topped off. Sometimes the level does still drop a bit, but not like before though. I'd imagine that should mean most of it is out of there are any?

Could you clarify what you mean by heat soak?

Yeah I might need to try that IR thermometer out there.