Changed thermostat, Coolant temperature stays at 185 degrees

[Donal]

Results are on Post 36

 

[SpaceBaller01]

Haven't we recommended an infra-red temp gun check at the thermostat housing, somewhere in this thread?

It has been recommended yes, I've got one now. I've been finding readings were around 140 - 160 when warmed up.

 

[SpaceBaller01]

So I've got it fixed. It was the sending unit after all. Since replacing it I've driven it down the road. Makes it right to the 205-210 mark.

 

[OR VietVet]

So I've got it fixed. It was the sending unit after all. Since replacing it I've driven it down the road. Makes it right to the 205-210 mark.

Perfect.

 

[BlaineBug]

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.

That's not necessarily true, your coolant temperature can exceed the rating of the thermostat. The rating of the thermostat is the temperature at which it is fully open (or possibly the temperature at which it begins to open, I am not sure.) However when 100% open your coolant can still increase in temperature considering that the heat dissipation of the radiator can't keep up with the load for whatever reason.

Years ago I remember a large debate on another JEEP forum regarding the purpose of a thermostat, and that it was to 1) Decrease the time it takes to reach optimal operating temperature for efficiency and 2) Decrease the flow of coolant to increase heat transfer to the radiator. Running NO thermostat at all can result in overheating as the coolant is moving too quickly to properly dissipate heat. Much arguments and debate ensued.

Air bubbles in the cooling system can also show funky inaccurate temperature readings too if the temperature sensor is in contact with an air pocket versus liquid coolant.

 

[mattbta]

So I've got it fixed. It was the sending unit after all. Since replacing it I've driven it down the road. Makes it right to the 205-210 mark.

You replaced the ECT sensor on the DS head?

 

[B-train]

That's not necessarily true, your coolant temperature can exceed the rating of the thermostat. The rating of the thermostat is the temperature at which it is fully open (or possibly the temperature at which it begins to open, I am not sure.) However when 100% open your coolant can still increase in temperature considering that the heat dissipation of the radiator can't keep up with the load for whatever reason.

Years ago I remember a large debate on another JEEP forum regarding the purpose of a thermostat, and that it was to 1) Decrease the time it takes to reach optimal operating temperature for efficiency and 2) Decrease the flow of coolant to increase heat transfer to the radiator. Running NO thermostat at all can result in overheating as the coolant is moving too quickly to properly dissipate heat. Much arguments and debate ensued.

Air bubbles in the cooling system can also show funky inaccurate temperature readings too if the temperature sensor is in contact with an air pocket versus liquid coolant.

I do agree with what you stated. A poor heat transfer through the radiator can increase the temperature. There are many variables in what can cause a temp rise - engine load, vehicle speed (airflow), A/C on or off, etc. A gunned up radiator will definitely add to the issues if that happened to be the case.

Air in the system can fool the temp sensor which is a thermistor that needs full contact with liquid to read correctly.

A thermostat temp is the open temp. It will then close slowly as cool anti-freeze fills the block and the process repeats. It's not like turning a switch on and off, it's a slower process. If it were stuck full open, depending on load, temp, airflow, etc the engine CAN overheat. If it's winter, the engine most likely won't reach operating temp and you will get the low coolant temp fault from OBD2. This is where a good IR gun can give you the temp delta between upper and lower hoses for diagnosis.

 

[SpaceBaller01]

You replaced the ECT sensor on the DS head?

Not sure on DS head, but it was the sensor between 2 spark plugs by the alternator.