B9 Thermostat Failure Tally

[AldermanToffee]

Really odd that it takes you that long to warm up.

What sensors did you replace? This motor has four coolant temp sensors. I am wondering if you didn't replace the correct ones? Or perhaps you have some frayed wiring?

It is very strange. The only possibility I’m considering right now is that the thermostat is potentially stuck open? Preventing the standard heat-up procedure as coolant is circulating the radiator.

Replaced the following sensors:
- Inner V temp sensor
- Cylinder head coolant temp sensor
- Engine block coolant outlet temp sensor

Haven’t replaced the radiator outlet sensor as there isn’t any issues with it afaik.

- - - Updated - - -

Also, replaced the wiring for one of those sensors that was frayed. The wiring is all good now, so doesn’t seem to be the issue either.

[qcrazy]

The thermostat would be a good possibility based on the control and the timing of the issue you are seeing. If the thermostat heater was bad, that could cause some of the issues you are seeing (e.g. fault out once it reaches operating temp)...
Screenshot_20221126-074410_Drive.jpg

But that doesn't really explain the implausible signals on the sensors. 🤔 Did you modify any of the temp control maps with your tuning changes? Weird one here. Best of luck, keep us posted!

[AldermanToffee]

The thermostat would be a good possibility based on the control and the timing of the issue you are seeing. If the thermostat heater was bad, that could cause some of the issues you are seeing (e.g. fault out once it reaches operating temp)...
Screenshot_20221126-074410_Drive.jpg

But that doesn't really explain the implausible signals on the sensors. 🤔 Did you modify any of the temp control maps with your tuning changes? Weird one here. Best of luck, keep us posted!

I actually just replaced my thermostat myself. It cost me £88 and took around 2:30 hours.

It has fixed the issue :)

The error messages from the ECU are utter useless and frankly counterintuitive. In hindsight the thermostat would’ve been the more obvious thing to replace had one of the other sensors not had a slightly frayed wire.

I’m glad that’s over and done with!

[AldermanToffee]

I spoke too soon, the issue is back lol.

I don’t think the thermostat was ever the issue. When I uninstalled the thermostat the metal seal that should’ve been pressed into the block fell out. I incorrectly assumed the seal should’ve been positioned around the thermostat instead of pressed into the block.

Due to this when I reinstalled the new thermostat I placed the seal around the thermostat prior to installing the thermostat into the block, hence the same issue now occurring.. the thermostat is not stuck open, rather the coolant is leaking around the seal.

I will take the car apart again next week and press the seal into the block, hopefully it alleviates the issue.

In the meantime I’ve found that driving the car as though I’ve stolen it keeps the coolant at a suitable temp to prevent the fans kicking on.

[spacecase]

Curious to see who all has replaced their thermostat and at what mileage. Also would like to know what symptoms you experienced when it failed.

-Taking a long time to warm up (oil temp <190* for 20 miles / 40 minutes of driving)

anyone know target oil temp for these cars? This might be normal as I don't hit 190 oil temp for a loooooong time after start-up, and usually sit around 180 after 15-30 minutes of highway driving.

[AldermanToffee]

anyone know target oil temp for these cars? This might be normal as I don't hit 190 oil temp for a loooooong time after start-up, and usually sit around 180 after 15-30 minutes of highway driving.

Anything above 180f if you’re just pooting around.

If you’re driving with a heavy foot anything up to 260f is normal, slightly hotter if on track for example.

[AldermanToffee]

Hello, me again.

I replaced the seal again today but pressed it into the block this time.

I can safely say the problem is resolved.. happy days.

[thermobryan]

Going to change mine proactively, at 75k now..

[AldermanToffee]

Going to change mine proactively, at 75k now..

To be honest I wouldn't bother seeing as though I got 97k out of mine and it was one of the first builds. You won't damage anything as long as you change it as soon as your car either:

- Stops heating up
- or shows a coolant too high warning

So unless you're planning on keeping the car for a few more years it might not be worth doing.

Saying that, it's very easy to do. I had a spare pair of hands the first change but I did it myself yesterday and only took two hours start to finish. Everything is super easy to get to.. it's probably the most rewarding thing I've changed/fixed on the car lol.

[thermobryan]

To be honest I wouldn't bother seeing as though I got 97k out of mine and it was one of the first builds. You won't damage anything as long as you change it as soon as your car either:

- Stops heating up
- or shows a coolant too high warning

So unless you're planning on keeping the car for a few more years it might not be worth doing.

Saying that, it's very easy to do. I had a spare pair of hands the first change but I did it myself yesterday and only took two hours start to finish. Everything is super easy to get to.. it's probably the most rewarding thing I've changed/fixed on the car lol.

I'm going to keep it long term for a few reasons. I'm just doing preventative work before failure.

[AldermanToffee]

My new thermostat has failed :)

Seems as though this also happened to another person on the first page of this thread.

Confirmed it was the stat by replacing the seal but car won’t come up to temp again.

Well.. I guess fourth time lucky next week?

[East_Coast_S4]

So I am gushing out Coolant everywhere it's been fun trying to pinpoint it - Apparently we have a thermo-pnuematic valve/secondary thermostat in another housing that controls flow from the head to the heater core. It is called a Coolant shut off valve.

06M-121-678-H

Mine the whole housing is split and cracked I am guessing whatever is inside broke. Blowing out a 1/4 gallon of coolant in less than ~100 miles. I will get more details when the parts come in and I get to tearing into the install. I have ordered both that and the new revision thermostat since I will be in there anyway.

[qcrazy]

It is this... Sucks if these start splitting. That would be a new feature Audi added.

Screenshot_20221105-144523_Drive.jpg

[Esmin23]

It is this... Sucks if these start splitting. That would be a new feature Audi added.

Screenshot_20221105-144523_Drive.jpg

Had mine replaced last year. It was leaking since new!

[qcrazy]

My new thermostat has failed :)

Seems as though this also happened to another person on the first page of this thread.

Confirmed it was the stat by replacing the seal but car won’t come up to temp again.

Well.. I guess fourth time lucky next week?

Did you ever get this sorted? Was it just a second bad thermostat?

[AldermanToffee]

Did you ever get this sorted? Was it just a second bad thermostat?

I did yes. Sealing ring again. It’s hammered in stupidly hard now and has been fine since.

[Jcv18]

I did yes. Sealing ring again. It’s hammered in stupidly hard now and has been fine since.

22 sq5 with 8k tuned since 3k. Was e85 over summer now back on 93 stg1 034 and immediately when I switched from e85 to 93 I got the stuck tstat code and it keeps coming back and o rarely get over 190 oil temp. Being this is such a known issue have any of you gone in to audi for warranty and they denied due to tunes or parts? I know there's an issue and I'm contemplating just bringing it to my indy shop vs getting denied and td'd at audi.

[KHobbes]

I'm about to go through the process next week. 2018 S5 SB coolant starting leaking. I'm at 120k miles and I have to top off the coolant levels about every 3-4 days with a coolant smell and a small coolant puddle on the garage floor. She's not overheating and the operating water temp is right where it should be, but after reading through the thread, I may have an issue with the coolant shut-off valve. Looking down into the engine well, there is fresh coolant on the lower-right of the engine between the AC compressor and the crankshaft pulley right below where the shut-off valve is located. With the number of miles and to be safe, I'll replace the pump, tstat, and shut-off valve. Should be a fun weekend.


Can someone help me out with the P/N for the Coolant Shut Off Valve in the red box please? Many thanks!

Coolant shutoff valve.jpg

[AldermanToffee]

I'm about to go through the process next week. 2018 S5 SB coolant starting leaking. I'm at 120k miles and I have to top off the coolant levels about every 3-4 days with a coolant smell and a small coolant puddle on the garage floor. She's not overheating and the operating water temp is right where it should be, but after reading through the thread, I may have an issue with the coolant shut-off valve. Looking down into the engine well, there is fresh coolant on the lower-right of the engine between the AC compressor and the crankshaft pulley right below where the shut-off valve is located. With the number of miles and to be safe, I'll replace the pump, tstat, and shut-off valve. Should be a fun weekend.


Can someone help me out with the P/N for the Coolant Shut Off Valve in the red box please? Many thanks!

Coolant shutoff valve.jpg

https://parts.audiusa.com/p/Audi_201...6M121678H.html

[KHobbes]

Thank you AldermanToffee!

[Dardani2000]

So I decided to change the oil from under the car this time and there was coolant look a like on the underbelly tray but there was oil leak allover the place. 2018 54k never tuned.

[sepangrs5]

My thermostat was stuck open and was replaced a few weeks ago- only at 70k miles. Also, I bought a racingline catch can and plan to install that soon! I know some ppl have had pcv issues


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[OverBoosted]

Mine thermostat just failed at 49,000 miles on a 2018 S4. It was stuck open with the radiator fan running at 100% when the car is on and also failing to get up to temp. The dealer mentioned it was covered under a California emissions warranty that runs 7 years or 70k miles.

Audi should really recall these at this point, there was a class action lawsuit for the 2.0T thermostat.

[Albertmald]

Mine thermostat just failed at 49,000 miles on a 2018 S4. It was stuck open with the radiator fan running at 100% when the car is on and also failing to get up to temp. The dealer mentioned it was covered under a California emissions warranty that runs 7 years or 70k miles.

Audi should really recall these at this point, there was a class action lawsuit for the 2.0T thermostat.

Hey OverBoosted, which dealer was this if you don't mind me asking? I have a '19 with 26k miles (I'm in CA) and believe my TStat has failed.

[Ordie]

Add mine to this list. 2021 @ 33k miles. Had the warning “Coolant temperature: too high. Please let engine run while vehicle is stationary” come up one day but it went away pretty quickly. 2 days later I notice the fans running full blast a block away from the house after first start. Then 10 minutes later the same warning. This time didn’t go away and AC not blowing cold. Turned around to get it home, halfway home oil temps were getting above 205 (never seen it above 202). So I started monitoring it and eventually reached 210. Knew something was odd so I limped it home. Audi had it for a week now. Was supposed to be ready today but just got a text from SA that coolant got into the vacuum system and more parts are needed.

[hotdogsandrice]

2020 S4 @ 55k miles. Code P0597 (Thermostat heater control circuit/Open with F265 code). Takes a long time for coolant temp to warm up and losing MPG. Gonna get it replaced along with water pump and coolant shutoff valve. Do the manuals in erwin show you how to take out the front end and procedure for replacing them?