2006 gmc yukon xl SLT 5.3 L thermostat

[Woodblocker55]

I took the thermostats out and it had paper gasket along with the rubber around thermostat.. so scrapped all paper off and installed ac delco thermostat with rubber gasket and that it ...scrapping paper off was nasty why was there a material gasket in there ? It's just supposed to be the rubber one right on thermostat right.??

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[2006Tahoe2WD]

Same thing happened to me yesterday. I took off the old thermostat and there was a crappy paper gasket falling apart in addition to the "O-ring". I replaced with just the new "O ring" sort of thing that came with the new (from dealer) thermostat. I think the paper gasket could mess things up? Did I do that? I don't remember.

 

[2006Tahoe2WD]

Update on new thermostat. I still notice the temp. falling on long downhill sections.
It sort of makes sense even if there is a working thermostat because there is no gas being burned and therefore no heat. At some point the temperature is going to go down. Maybe is didn't notice the drop before, IDK. Well at least I don't appear to have created leaks. That's an accomplishment.

 

[Marky Dissod]

Update on new thermostat. I still notice the temp falling on long downhill sections.
It sort of makes sense even if there is a working thermostat, because there is no gas being burned and therefore no heat.
At some point the temperature is going to go down. Maybe i didn't notice the drop before, IDK.
Well at least I don't appear to have created leaks. That's an accomplishment.

If your '06 has electrical fans that have not been reprogrammed, then GM's hotter-than-necessary fan-on thresholds are still in effect.
So, when you go downhill, even if the engine does not go into DFCO, (essentially, the road spins the powertrain via the wheels, instead of the other way round), so little fuel is required and the engine load is so low, that the engine temp goes down toward the thermostat' opening threshold.

In fact, if it's cold and wet enough outside, and you don't have the little restrictor in the radiator, the thermostat can even start to close a bit.