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Here's what I'd do if it were mine. I'd take it to a performance/dyno shop. Install a 160 stat, have it dyno tuned (they will adjust your fan temps), flush the system-problem solved.
Unfortunately we are under warranty and can do so much. Might as well let the engine blow so we can get a new one. Either we live with it or trade cars and take our loses. This is a serious issue. So far my solution is shut the engine down which re-sets the computer and turns the fan on high. Terrible plan when sitting in heavy traffic. Try dealing with that scenario.
Does turning the AC on have any effect when the fan is not running? The AC system will also command the fan on since it is needed to pull air across the condenser. If the radiator cooling fan doesn't come on when the AC is operational then this rules out a single sensor since that commanded operation is different than that from the coolant sensor.
Because you find the fan will sometimes come on when stopping and then re-starting the engine a fan relay would be the most likely suspect. Because you are seeing both increased coolant and oil temperatures that rules out a indicating gauge/sender issue since it is highly unlikely both of these separate indicating circuits would fail together creating a false indication of an overheat condition.
This is what I was gonna mention. I used to have a 4th gen TA and you had to run the AC in stop and go traffic or you'd overheat.
No word yet from GM or the dealer. Its been at the dealership for a week now so hopefully they are figuring something out. The dealership seems to be putting in a lot of effort on my behalf.
I just had a serious overheating on my 2014 yesterday. In a matter of a few minutes, it went from normal temp to pegging the gauge and blowing coolant out of the reservoir. Dealer cannot replicate problem so far.
They replaced the radiator fan assembly and it is still doing it, I'm going to take the loss and trade it in on a different vehicle. It's rough because I love everything about the car but I cant have unreliable transportation.
I had an overheating problem that service could not duplicate. There is a service bulletin (PIP5176) that says to replace the coolant manifold assembly.
There was an issue with the 14s that involved the fan and fan controller. The symptoms were driving along on the interstate, hit a traffic jam or exit at a light and the car would start to overheat. The fan should be screaming but the fan wasn't coming on. If you turn off the car, open the door to drop the RAP, then close the door and restart, the fan will come to life and start cooling the engine. The only fix we found was to replace the fan and controller with the Z06 fan and controller. I had the issue, changed the fan/controller and the problem is gone.
Elmer
Last edited by eboggs_jkvl; Sep 13, 2019 at 08:07 PM.
There was an issue with the 14s that involved the fan and fan controller. The symptoms were driving along on the interstate, hit a traffic jam or exit at a light and the car would start to overheat. The fan should be screaming but the fan wasn't coming on. If you turn off the car, open the door to drop the RAP, then close the door and restart, the fan will come to life and start cooling the engine. The only fix we found was to replace the fan and controller with the Z-6 fan and controller. I had the issue, changed the fan/controller and the problem is gone.