OK guys I have some questions related to the "normal" operating temperatures of a 2019 GS. Up until about 2 weeks ago in normal street driving my car would warm up to above 180 (thermostat temperature) and then would vary some depending on ambient temp and air conditioner status. I live near Phoenix AZ so in the summer, all temps are about 20-30 degrees higher.

Lately, with ambient temperature anywhere from high forties to mid seventies the car when moving 45-55 only warms up to 174-178 until I stop and then will start to get warmer reaching 180 ish at a normal stop light time. If I stop for longer I have seen temps near 201. The fan is operating but does not change speed. with changes in coolant temp even if the air conditioner is turned on.

I believe I have a cooling system issue, maybe more than one based on the fact that the engine never gets to thermostat temp when moving, and when the temp drops to 174, the redline drops to 4500.

I brought it to one dealer that didn't try and diagnose through a miscommunication about the redline, and now the second dealer says, "our scans don't show a code so the car is operating per design."

My issue with that is the car is operating different than it was 2 weeks ago.
OK, the questions. For folks that live where the winter temps normally get colder than phoenix, what is your normal operating temp during the winter? Does your redline keep changing from 4500 to 6500? Does the engine get warmer than mid 170s?

 

Your coolant thermostat is defective. When cold, It does not close completely.

 

I'm at the dealership today to have my thermostat replaced as I have similar symptoms. It's looks like an easy job to replace but as my 2019 GS is under warranty I'm having the dealership perform the replacement.

 

The stock thermostat is set at 186 deg. My Z06 will run in traffic at 188 deg in the current ambient Temps that are in the mid 40s to mid 50s.
In 70 deg weather on the highway at a constant 70 mph it will bounce between 188 and 192.

It sounds like your thermostat isn't closing all the way but isn't bad enough to set a code yet. Dealership won't fix without a code.

Bill

 

Thanks for the replies. Here is the outcome from the dealer. One, the service writer didn't put the correct stuff into the service request. To quote "Customer states temp never gets warmer than 180 at idle" That is NOT what I told him. I specifically told him the temp WOULD go up at idle, but at normal cruising speed, it drops down below 180.
The outcome was from the tech: "npf thermostat opens around 187 this is normal operation and no codes are found"
So I guess I either pay an independent shop to replace the thermostat or I wait for a hard failure and potentially have to tow to the dealer. Not a hard choice.

 

You should have the thermostat replaced, operating the engine when it is running cooler than it was designed for can result in increased cylinder bore/ring wear.

 

I had an occasional "coolant and oil temps drop 20'F from normal" problem on our 2017 Z51. Dealer couldn't find any codes or problem, since it was intermittent. So when I had the coolant drained/refilled last Fall, I told them to replace the thermostat on my dime. They replaced it and charged it as a warranty repair without further discussion.
A friendly dealer can be helpful...

 

My dealership replaced my thermostat even though there weren't any codes.

 

Under warranty or did you pay for it?

 

What's a thermostat running these days?...10 dollars? If I had any concern whatsoever with a malfunctioning thermostat I would replace this myself. It's an easy fix. Easier than an oil change. Will cost about $10 and a hour of your time which mostly will consist of cleaning up the mess.

 

The same happened to me. Drive on highway yellow band returns and temps drop. T-stat stuck open. Go and get it replaced so you can get your oil up to operating temps. Operating temps matter more than you think.

 

Covered under warranty.

 

If the dealer won't replace the thermostat under warranty, just do it yourself (or find a friend who is mechanically inclinded if you are not).

 

I'm capable, just don't have any way to get the car in the air and I'm sorry to say I'm a tad thicker than 6 inches. I know thermostat is accessed from on top, but radiator drain maybe not.

 

Don't you own a race ramps? Vehicle just needs to be high enough so you can open the radiator petcock.

 

I don't own race ramps or any other way to jack this car. I do have a friend with a four post lift that volunteered to let me use it. That is probably what I'll do.

 

Thermostats are basic, very cheap commodities. I once had to replace one because a part of the sheet metal it was stamped out of broke in half, leaving the valve stuck partway open. The most time consuming element of the replacement was cutting a new gasket out of a sheet of gasket material. With a ready-made gasket it would have been maybe half a hour at most.

If it's under warranty let the dealer fix it while you wait.

 

Normally I would agree that thermostats are very cheap, but not if I want to use oem. All the chevy car parts places that I've checked online only sell a kit that includes the thermostat, the o-ring and the housing. Right around $70 for discounted places to about $125 for oem price. The part number is: 12674634 is called a water outlet and looks like this:

Thermostat is integrated into the housing. On my car the housing appears to be plastic,

 

It's a bit different than plastic, but to your point....it's not metal.

That aside....There's no need to drain the radiator. The thermostat is high enough up on the engine that very little coolant will drain out. If you're concerned. put some towels under the thermostat and rinse/clean the area after you install the new one. It is a bit easier if you remove the air intake from the throttle body so you have more room to work.

If you insist on draining coolant, you reach the petcock from above, it's on the driver's side. They're often difficult to turn, so a pair of pliers helps with leverage. You'll need a very flat (couple inch high) catch pan for it to drain into or simply drive the car up on a couple 2"x10" boards....or 2"x4"s for that matter. It's not rocket science.

 

Thanks for the advice. I will probably post my take on changing the thermostat when I've finished the project. It's not a top priority project so it may be a little while.