New thermostat overheating

[MAGAlomaniac]

2015 Tahoe lt. it was not coming up to temp so I replaced the thermostat and coolant temp sensor. Now it gets hot(220 -260) and the hose coming off the thermostat remains cool. I’ve got a Chevy thermostat on order. What else could this be?

 

[B-train]

Have you run it with the overflow cap off until the thermostat opens? Try squeezing the upper hose while running to see if you. An encourage any trapped air to move out. Lastly, double check with an IR temp gun on the upper hose, lower hose, and other coolant hoses to see what they are running for temps.

 

[OR VietVet]

What @B-train said. Sure sounds like that. Plus, get a better thermostat and then get the air out of it. Going to 220 degrees, is not worrisome to me but 260 is...

 

[Marky Dissod]

Going to 220F is not worrisome to me but 260F is...

With aluminum heads, I start looking to pull over @ 221F, by 230F I better have pulled over already.
Part of my pcm's tune is that it starts acting like it's already overheating @ 230F, to buy time.

 

[k_arnold72]

Did you possibly get a thermostat with a different temperature rating? If you get a lower temp thermostat without adjusting everything to work with it, this can be the result. Has happened to me before. If you have the oem spec 207⁰, disregard.

 

[MAGAlomaniac]

Have you run it with the overflow cap off until the thermostat opens? Try squeezing the upper hose while running to see if you. An encourage any trapped air to move out. Lastly, double check with an IR temp gun on the upper hose, lower hose, and other coolant hoses to see what they are running for temps.

I heard since the reservoir is the high point it will self burp. I tried bringing it up to temp with the cap off, no air came out. The upper hose never got hot even after the temp went over 220. The lower hose was hot to the touch. It’s got to be the thermostat right?

 

[OR VietVet]

Thermostat has to open to get heated coolant to transfer to radiator.

 

[B-train]

With a hot lower hose, you have a blocked thermostat. Replace with GM OE Parts

 

[Fless]

Back up a minute... why was the coolant temp sensor changed? Are we sure that that new one is reporting correctly?

 

[89Suburban]

You can’t just burp these out at standard idle. You need a few good random mid range revs to get the heater lines totally purged.

 

[MAGAlomaniac]

Back up a minute... why was the coolant temp sensor changed? Are we sure that that new one is reporting correctly?

I changed it because it wasn’t coming up to temp at all and the fan would come on.

 

[MAGAlomaniac]

I changed it because it wasn’t coming up to temp at all and the fan would come on.

I think it’s reading correct because when it says the engine is too hot the top hose is a lot cooler than the bottom one. To me that means the thermostat is stuck closed.

 

[MAGAlomaniac]

You can’t just burp these out at standard idle. You need a few good random mid range revs to get the heater lines totally purged.

Ok, I’ll try that. Would the air come out just by driving it or do I need to bring it up to temp with the reservoir cap off?

 

[Doubeleive]

Ok, I’ll try that. Would the air come out just by driving it or do I need to bring it up to temp with the reservoir cap off?

been seeing a lot of bad thermostats out there particulalry for this gen, It comes up at least every couple weeks on here. GET that oem one in.

 

[buckwild27]

Here's a few options. If the thermostat is the issue and you want to run a cooler temp and not have to do ecm tuning.

Katech 174 Degree Gen 5 LT Thermostat

For LT1/LT4/LT5/L83/L86

katechengines.com

If you want to get away from this generation of thermostat you can get this housing and run the previous generation thermostat.

DMS Billet Thermostat Housing w. LS3 Style 160 Degree Thermostat - Gen V LT

DMS Billet Thermostat Housing w. LS3 Style 160 Degree Thermostat - Gen V LT (DMS160LT)

www.montmotorsports.com

And in the off chance it's not the thermostat you can remove the thermostat and run it without to determine if a head gasket is leaking. This will throw a check engine light because the thermostat is out. But you will know you have a bigger issue if engine over heats with out a thermostat. You will have to drive it to determine this.

 

[89Suburban]

Ok, I’ll try that. Would the air come out just by driving it or do I need to bring it up to temp with the reservoir cap off?

Do the original burp with the cap off.

 

[StinkyLinky8]

I feel like I had the same issue recently. For a while, I noticed the engine failing to come all the way up to temperature and maintain that temperature sometimes it would but it would back down. Replaced the thermostat and it was coming up to temperature and holding, but didn’t seem like it was opening quick enough as I would get on the highway and wide open throttle and it would start to overheat and then suddenly the temp would go back down to normal I went back to the auto store and got another thermostat and replaced it and since then it has been fine.

 

[Doubeleive]

optionally you can test the existing thermostat in boiling water....

 

[yugrus]

I had good luck with the vacuuming tool that pulls air out of the cooling system before filling it with coolant. It has worked every time so far, no air pockets. I will use it again soon when I replace the pump, the hoses, etc. as a preventive maintenance.

 

[Doubeleive]

my money is on bad thermostat, 99% percent of the time that's what it is when people use a aftermarket on these k2's
not sure why other than there seems to be a crap-ton of bad ones out there. It gets posted on here all the time.......