Changed thermostat, Coolant temperature stays at 185 degrees

OR VietVet said:

Crickets are a PITA.

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My apologies, I thought I set this to notify me when I got a reply.

B-train said:

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.

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This is a 2004. Unfortunately the thermostat has no degree rating on it. I just know what I put in was 185, from the Amazon page. I'll have to give them a call on that one.

I do have another thermostat I ordered (but forgot to return, it's Gates (185°) instead of GM. I could try this one, but I'd rather not dump the coolant if I don't have to from changing the thermostat.

Fless said:

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.

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Unfortunately I have no idea. Bought the truck earlier this year with virtually no history. I'll try that return line trick though.

THarber said:

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

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Nope that's wayyy too ahead of the stuff I do lol

It went to temp a few.months ago then noticed it stopped going up all the way (before the weather started cooling).

MassHoe04 said:

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...).

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Honestly I'd be surprised I pretty much followed it as It came out. Has not overheated at any point. It did go to temp on like the 2nd or third time I drive it after Installing it a day or two after. But hasn't come back since.

SpaceBaller01 said:

Honestly I'd be surprised I pretty much followed it as It came out. Has not overheated at any point. It did go to temp on like the 2nd or third time I drive it after Installing it a day or two after. But hasn't come back since.

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Yeah... I wasn't insulting your mechanical abilities. I haven't found out if the casting for the thermostat housing would even allow the part to be flipped like it could on the Jeeps. I was just trying to talk out some of the possibilities and an open stat was one of the things I was thinking of as at least being remotely possible. Even then, the engine would get up to the normal operating temperature of somewhere close to 210 F +/- a few...

Cooler than normal most all the time and occasionally almost normal random other times.
This is a head-scratcher, but I am sure someone can help walk you through this diagnosis.

Does this have electric cooling fans, or a clutch fan?

SpaceBaller01 said:

Could you clarify what you mean by heat soak?

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A heat soak takes place every time you get the engine to operating temp and then shut off. The engine temp climbs higher then because there is no air flow. Then when it hits its peak temp, it drops. If you have electric fans they can stay on after shut engine off till a temp sensor sees the temp drop to a certain point.

Fless said:

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

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Hee-haw was always on after the Dukes Friday night when I was a kid. I was too young to pay attention to skimpy dressed ladies.

Here's another to show my age....Pennsylvania 6-5000! I'm middle aged, but old soul'd.

My bets on too cool operating are also on missing restrictor.

So, running with the cap off at operating temp will allow coolant to flow freely and encourage air pockets to move through the system. Running the rpm up to a steady 1500 to 1800 rpm for about 5 minutes helps as well.

Heat soak is shutting down the motor hot (preferably after higher than idle rpm). It allows the engine heat to increase due to lack of coolant or air movement. Basically it allows fhe coolant to "grow" due to the increase in temp, therfore giving you a hot reading that can be topped off as needed.

An IR gun will verify this as well.