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... So far every place says out of stock or not available.
Not so on sites like GMPartsDirect. They usually annotate the listing when things aren't available, special order, etc.
 

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Does anyone know where I can get a replacement thermostat? I have a 2019 GMC Acadia V6 with 60,000 miles with same issues as everyone else. Steering assist reduced, no AC, gauge drops to cold and fan is blowing on high. We have already replaced the sensor and it still does it. Next step is going to be battery and thermostat but we cant find a thermostat ANYWHERE.
I believe the thermostat replacement would be covered under the new car power train warranty. Why not have the dealer's service center do it for you?
 

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Does anyone know where I can get a replacement thermostat? I have a 2019 GMC Acadia V6 with 60,000 miles with same issues as everyone else. Steering assist reduced, no AC, gauge drops to cold and fan is blowing on high. We have already replaced the sensor and it still does it. Next step is going to be battery and thermostat but we cant find a thermostat ANYWHERE.
Apparently it is GM 12678779 . . . . but also has 15-11122 on the OEM label .
You can try GMparts Outlet as suggested
. Perhaps they have it. . . or perhaps not.

Below is a video of the 2017 GMC Denali (not Limited models) with the LGX 3.6L engine.
This is the same as +2017 C1xx models to date so far as of this writing.

That thermostat is a task to get at so for future readers, this may help.

 
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Um. . because @LaurynDixon is asking where to get the part.
"The Lord helps he who helps himself" The member was given enough info (part number and sites) to find what they need on their own. The internet has many sources from which to chose. I strongly suggest using GM parts sites.

So apparently you can really find one either?
I don't (and won't) do things like that at the behest of a forum whore like you.
 

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Apparently it is GM 12678779.
You can try GMparts Outlet as suggested
. Perhaps they have it. . . or perhaps not.

Below is a video of the 2017 GMC Denali (not Limited models) with the LGX 3.6L engine.
This is the same as +2017 C1xx models to date so far as of this writing.

That thermostat is a task to get at so for future readers, this may help.

We see several thermostat parts for a v4 but can’t find any at all for a v6
 

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We see several thermostat parts for a v4 but can’t find any at all for a v6
That number is listed on many GM parts sites as the thermostat for 2019 3.6L V6 engine and is the very same one shown in the Youtube Video minus the extension pipe.

2017-2021 GM Water Outlet 12678779 | OEM GM Parts
 

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Yes. . I've seen the both the OEM and aftermarket thermostat itself. . without the attached extension pipe at several online outlets.
The thermostat assembly with the extension pipe shows up as not available and out of stock at many sites.
In any case, if you viewed the video, just the thermostat itself can be replaced with less disassembly and no fuel rail removal. Still a tight fit, getting at the bolts, but doable.
 
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I just had the thermostat on my 2017 Acadia replaced. 80,000 miles, dealer serviced since I bought it new. $2000 for the parts and labor. This vehicle has had electrical issue after issue since I bought it. Most unreliable vehicle I’ve ever owned. What is the logic of a failed Thermostat reporting “Steering assist disabled. Please drive carefully” relating To your engine overheating? Isn’t that what your temperature gauge is supposed to indicate for you? I drove around for 3 days figuring the steering didn’t feel any different, so it must not be that big a deal. Come to find out, the radiator was nearly dry by the time I could get it to the dealership.

One thing I know is I will never by another GMC. I had junkers in high school and college that were more reliable than this Acadia.
 

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I just had the thermostat on my 2017 Acadia replaced. 80,000 miles, dealer serviced since I bought it new. $2000 for the parts and labor. This vehicle has had electrical issue after issue since I bought it. Most unreliable vehicle I’ve ever owned. What is the logic of a failed Thermostat reporting “Steering assist disabled. Please drive carefully” relating To your engine overheating? Isn’t that what your temperature gauge is supposed to indicate for you? I drove around for 3 days figuring the steering didn’t feel any different, so it must not be that big a deal. Come to find out, the radiator was nearly dry by the time I could get it to the dealership.

One thing I know is I will never by another GMC. I had junkers in high school and college that were more reliable than this Acadia.
Mine does that as well everything I looked up with that message pointed to the coolant temp sensor itself alot of times they just replace both
 

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My 2017 Acadia is doing the same thing. Everything I have found leads to the Engine Coolant Temperature Sensor. It isn't hard getting to the sensor, but can't figure out how to get it out. I think I have to remove the Thermostat to get a socket or wrench on the sensor. Does anyone know if I have to drain the coolant before opening the thermostat? If I just have to drain a little, where should drain it from?
Mine was also doing that the thermostat is really hard to find right now so I just replaced the sensor now yhe fan is stuck on high speed and steering assist reduced light on . They show the same symptoms but in my case it's the thermostat which I can't find
 

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So is the 12678779 and the duralast 86021 the same prt then? They look identical
WOW!!!
$1400 for the thermostat.
I had no idea that is what the repair runs at the dealer.
Is it under manifold I have had mine apart twice once because wrong part and the 2nd time I replaced sensor no luck with thermostat can't find it. You have to take off the engine( manifold off it's not the easiest job but can be done with the right tools
 
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