Which Aftermarket Thermostat? (no OE's available??)

K2xxSteve · November 30, 2023

Hi all,

First real issue on my 2018 Suburban 5.3L at 86k miles. On a road trip over Thanksgiving, I noticed it wasn't holding operating temps. It has always stayed dead nuts on at 210F indicated no matter what (hot/cold/towing), but on this 900 mile trip it was fluctuating between about 190 to 205F indicated. It would touch 210F and never go above that going up a long grade or if I had to get on it to pass someone, but otherwise kept fluctuating between 190-205 indicated. My thoughts. Thermostat stuck open, and will open as much as it needs to to avoid overheat, but won't close up for whatever reason resulting in a mild underheat and very slow warm-ups.

Took to dealership (I hate these guys), they offered to throw a temp sensor at it (???). Saw here on the forum that these can go bad too, so said okay but was wondering. Honestly, I just wanted to throw money at it and make the problem go away also, but sure enough it's doing the same exact thing today so just wasted a bunch of money for nothing.

Digging in now, and apparently NOBODY has the OE thermostat in stock??

GM GENUINE PARTS WATER PUMP OUTLET ASSEMBLY WITH THERMOSTAT
GM Part # 12674639
ACDelco Part # 15-11125

Not online parts sources (RockAuto, O'Reilly, NAPA, etc.), and not local dealerships either, hence offering to throw a temp sensor at it and hoping it would fix it, since they apparently didn't have any thermostats (GM Parts online says no for all area dealership, but still trying to get in touch with the parts counter guy to confirm.)

What gives?? Is there any place you can get the OE thermostat from these days?

Summit Racing listing actually showed an estimated shipping date of MARCH 2024? What the actual f*??

https://www.summitracing.com/parts/ado-15-11125

Rock Auto had these MOTORAD thermostats available? Are these any good? I searched and found one thread here where someone who got the stock 207 degree t-stat reported the engine running too hot, and actually had to get the cooler one and then it was fine. No idea if that's the norm or just a fluke? What else is there?

https://www.rockauto.com/en/catalog/chevrolet,2018,suburban,5.3l+v8,3438969,cooling+system,thermostat,2200

Also, for those of you that have scan tools, if the gauge is showing 190-205F indicated, do you know what the actual coolant temps are for that? I'm assuming the gauge stays parked at 210F across a wider range. Just wondering. Going to be putting 2-3k miles on the truck over the next month, so want to get this sorted ASAP without getting ripped off again, or having to put a flakey part in.

Thanks for the help!

Edited November 30, 2023 by K2xxSteve

K2xxSteve · November 30, 2023

UPDATE finally got through to the parts counter guy at my dealership. He confirmed the parts are "massively backordered" and that they have 8 on backorder right now, but no idea when they're coming in. FFS.

CarFan1 · December 2, 2023

Is it really going to be like this to get parts for a 2015-2020 Suburban? Ours is barely 3 years old and knock on wood we've not had any issues except for sluggish automatic side steps. And we'll be making our last payment before spring of next. But is a parts shortage just going to be part of the ownership experience?

K2xxSteve · December 4, 2023

On 12/2/2023 at 6:06 PM, CarFan1 said:

Is it really going to be like this to get parts for a 2015-2020 Suburban? Ours is barely 3 years old and knock on wood we've not had any issues except for sluggish automatic side steps. And we'll be making our last payment before spring of next. But is a parts shortage just going to be part of the ownership experience?

I think it's due to the strikes, to be honest! Saw this on a parts website. I might just have to put the questionable MOTORAD in it for now.

K2xxSteve · December 4, 2023

Additional troubleshooting steps over the weekend, and trying to 100% confirm the issue and that it wasn't something else before I dump more money into this. Got an OBD2 reader and a new laser temp gun, and monitored reported coolant temp sensor data vs. head temp (should match), thermostat inlet temp, and then thermostat outlet temp on the radiator hose in 1 minute intervals on a cold start. Saw thermostat opening way early at 160F. Not sure when the stock is supposed to open, but either way it's opening early, and staying open below where it should, thus the truck is not maintaining temperatures. Done deal it's the thermostat, which is what I had thought it was in the first place! The coolant temp sensor was probably always fine!

Edited December 4, 2023 by K2xxSteve

K2xxSteve · December 4, 2023

Next problem has been finding where I can get a genuine GM thermostat assembly from. It appears this is a very common issue, which combined with the GM strike, has lead to widespread parts unavailability.

A couple days getting run around and ripped off by the dealership, and then a couple days genuinely trying to be helpful run around by a local shop asking legit questions making sure I wasn't fixing the wrong problem before I dump more money into it, and the two that had been found are gone. The local shop (good guys) had found an OEM part last Thursday but now gone, and a part my buddy had found at a parts store down in GA (I'm in MD) was also gone. F me!

Sooo.... off to eBay I go. I'm not sure where and if this is the same seller or not, but I'm 99% sure I had seen a post somewhere about these being legit. Someone here had ordered one somewhere. Per the description, they're new OEM thermostats off of the water pump assemblies. After reading a lot of bad reports here about the MOTORAD's being unreliable and/or not maintaining the correct temperatures, I feel safer buying this than the MOTORAD, so will see how it goes and report back!

Listing link is here. There were 6 left, now 5 after I purchased.

https://www.ebay.com/itm/115727184809

K2xxSteve · December 4, 2023

This is off that listing. Has GM and correct part number stamped into the housing. I bought another one that was listed as a Genuine GM part from another seller just in case. If the first one works out and I don't end up needing the backup, will either return it or re-sell it here in the FS forum.

What a CF!!!!

Grumpy Bear · December 4, 2023

More Information for GM GENUINE 1511113 (rockauto.com)

One left when I looked. This is the 194 F GM from the Cadilac and Corvette V8.

K2xxSteve · December 4, 2023

1 minute ago, Grumpy Bear said:

More Information for GM GENUINE 1511113 (rockauto.com)

One left when I looked. This is the 194 F GM from the Cadilac and Corvette V8.

Thank you, Grumpy Bear! Have seen your posts in a bunch of the other thermostat related threads here, which were very helpful! Good lead. So I have two of the 207 F OEM on the way (15-11125), but this might be helpful to someone else reading. I wasn't sure what the OEM prices were, but figured what I was paying on eBay was about on target.

Just curious, but which Cadillacs do the -13 PN / 194 F rated go into?

Grumpy Bear · December 4, 2023

1 hour ago, K2xxSteve said:

Just curious, but which Cadillacs do the -13 PN / 194 F rated go into?

2014-2017 CTS-V 6.2 Supercharged. [2016 shown]

K2xxSteve · December 13, 2023

So the new thermostat came in on Thursday and took it to a good local shop on Monday. Just short trips on Monday, but finally had a nice 40 minute drive today and it seems solid. Mostly stays dead-on at 207F actual in light driving and 50 degree outside temps. Forgot to take a photo of the one that came in, but it was a genuine GM part complete with GM and part number stamping, taken from a full water pump assembly as described in the eBay listing.

What a freaking hassle, but glad it's finally fixed!

The guy on eBay still has plenty of these if anybody needs them. $199 is a ripoff (I paid $149) but it is what it is when you can't get them elsewhere: https://www.ebay.com/itm/115727184809

You can get the full water pump assembly from which he's taking those from for only $50 more from Rock Auto, and elsewhere. Just remove the thermostat if that's all you need, and sell the water pump or keep it as a spare.

https://www.rockauto.com/en/moreinfo.php?pk=10622996&cc=3438969&pt=10178&jsn=492

40 minute drive log attached. It's working as it should so not going to do another cold start test and waste more gas.

mikemcclain8 · January 18, 2024

Just to piggy back in case anyone is searching and finds this post.

2015 suburban with temp gauge not going above 170 degrees and heat blowing warm only. Outside temp was 0 degrees. Went to autozone and picked up a thermostat for $55, installed in less than 30 minutes and temp back at 210 degrees with heat blowing very hot. Not OEM, but so far so good.