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2017 Chevy Silverado Thermostat Running Cold

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Okay so I broke my foot a last month so my truck has been sitting during the winter. Just recently the check engine light has came on. 


I used my code reader and is said the thermostat was running cold. 


And the engine fan automatically comes on and stays on for a little even after I turn the truck off. 


My question is there a simple fix to this? Or would this require a replacement?

Edited by HuntedOne4
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Was the code P0128?


The thermostat replacement is very simple, can be done in 10-15 minutes to be honest.


It's just two hoses and a few bolts that hold it down. You'll lose some coolant on a cold engine but not gallons or anything. Top off the coolant tank when you're done and that's it.



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I'll be doing exactly this job in a few days, but went with a 194* opening temp 'stat instead of the stock 207* stat.


My truck did NOT produce any DTCs nor driveability concerns, apart from being a little thirstier than before, and not completing the EVAP OBD2 test cycle (but no DTCs or dash lights for that).  My gauge needle moves between the two marks to the left of center (1/4 and 3/8 if it were a fuel gauge), and monitoring with a scan tool showed a maximum ECT of 170*F over the course of a 25 minute drive at 41* ambient air temp.; most of the time, ECTs stated in the 162-167*F range.

Edited by 16LT4
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Replaced the T-stat with 194* Motorad and took it for a test drive. Whereas before the truck spent most of its time in the mid 160*s over a nearly half hour drive, now it gets to 195* within 4 miles/under 10 minutes. The gauge needle also sits in the middle where it’s supposed to. I haven’t checked fuel trims, but they were negative before, so I’m going to wager they’ll trend upwards as well. 

What’s interesting is that I suspected bad T stat 2 years ago and had dealer look at it (under warranty) with negative fuel trims also, but they said it was fine. I never checked ECT at the time. Looks like I’ve had a bad T stat for a few years. I’m very curious to see if my fuel mileage improves now. 

At the same time, because more grounds are never enough, I added another main ground cable from the water pump to the chassis. 


Edited by 16LT4
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@16LT4 I might be interested in changing my thermostat as well. Can you provide the Motorad part number that you installed? Thanks


I think I figured out which one. I scoured for a long time but couldn't find a 195⁰ one for the 2014+ Silverados, just earlier model fitment. I finally jumped over to my go to that I forgotten about... There I came across the Motorad 194⁰ thermostat and a part # of 815194. Alternate 815-194. I'm guessing this is probably it???


Edited by mikeyk101
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18 hours ago, mikeyk101 said:

@16LT4 I might be interested in changing my thermostat as well. Can you provide the Motorad part number that you installed? Thanks


I think I figured out which one. I scoured for a long time but couldn't find a 195⁰ one for the 2014+ Silverados, just earlier model fitment. I finally jumped over to my go to that I forgotten about... There I came across the Motorad 194⁰ thermostat and a part # of 815194. Alternate 815-194. I'm guessing this is probably it???



Yes that's it.  194* not 195*, my error.  I edited my earlier post.


No scouring needed; readily available on Rock Auto without intensive searching:



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Is there any symptoms to a stuck open thermostat? Ok, my truck was running a bit cold today. Outside temps started around 26-28⁰. The gauge never hit 210⁰. Because it was running cold, I plugged in my OBDII reader while driving to see what the actual temp of the coolant was. It stayed mostly around 168-175⁰. And this was also after traveling at expressway speeds for about 45 miles each way. It did briefly hit 185⁰ when I was entering expressway in way back. I had myrtle the turtle in front of me casually merging and I sped up to get around her with full throttle. After getting up to a constant speed, it backed back down to around 173. After getting off expressway for some side road stop and go, it actually dropped to lower 160's to upper 150's but then got back up to upper 160's. 


I usually drive with my Range AFM delete but unplugged that to used the OBD reader as I didn't have my splitter cable so I could only use one at a time. So I was running between V4 and V8. I just never noticed it doing this before. I've had it sometimes take a short while for temp gauge to get where it should be or maybe even drop off slightly but not like this. I did check for any fault codes and there was none pending or set. And I didn't notice anything unusual with the radiator fans either. Not sure that they were even turning on...

Edited by mikeyk101
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2 hours ago, CamGTP said:

Those are the symptoms, never getting above 190 basically means it's stuck open.

That's kind of what I thought but figured it was best to ask. Now I really need to get that new thermostat. And of course for at least the next week or so, it is calling for the coldest temps of the year so far here. Not enough room to get the truck into the garage. Yay me!!! 

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Ok, I found the Motrad 815-194 on Amazon shipped to me for a couple dollars cheaper than Rockauto and will be here Wed. @CamGTP your post above says it's a pretty simple job so I'm gonna trust you. Just a quick question. Do I need any kind of sealant for the install? Looking at photos, it looks like there is a rubber o-ring. Can I just assume that I would need to dab some antifreeze in that ti lubricate then just torque it down? Also any idea on the torque values for the bolts?

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You don't need a garage, with some gloves on in the sun it's a quick job with the right tools.


No sealant, it's all o-rings. I have no idea on the torque spec, they are really small bolts so the torque spec is likely less than 10-15 ft/lbs. I just make them hand tight and snug them down.


It was -10 to -12 this morning here, plenty cold but warmed up to around zero which was nice.

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Slight hijack (sorry op). I did the trans thermostat change to the revised GM one a year ago. Ever since then, the engine runs cooler and the temp gauge is rarely in the middle. Is this to be expected and do I need to change the engine thermostat to the one mentioned in this thread?

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I'm about to jump in and do this probably over the weekend as temps mid-day should be in the 30's. I've been watching all kinds of videos and reading threads so have a pretty good idea on how I'm going to tackle this.


But after finding all of this, I still have a question. I've seen it done by just installing complete new assembly or by just disassembling old housing and just swapping the thermostats. I like the idea of using the new assembly because it seems like I can do it quicker. I plan on clamping large hose to minimize coolant loss. The new assembly has an o-ring but haven't been able to get a look at old housing. On most of the videos, a gasket is visible in the opening after old thermostat housing removed and I can't tell if it's supposed to be part of the old housing. I have seen the installation done both ways and some leave that gasket in place and some remove it. The gasket in the videos appears to be a thin, wide, circular gasket and not quite an o-ring. It seems to not only fit into the outlet but into the old thermostat as well. The o-ring on new Motorad thermostat appears like it would fit on flat face on top of water pump.


So @CamGTP should I be removing that old gasket or leave it in place? 

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3 hours ago, CamGTP said:

The gasket stays on the thermostat itself, just remove the old theremostat and replace it with the new one.

I guessing that the gasket should stay on the old thermostat but on quite a few of the videos, the gasket or what I think is the gasket stayed in the water pump outlet. Here is a photo off one of the videos I watched showing what I'm talking about.




And I have seen some say to leave it but most seemed to say to remove it. So just for clarification, I remove it and just go with the new o-ring attached in underside of new thermostat?

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