B9 Thermostat Failure Tally

[TheMysticWizard]

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.

I've read a few instances of people having them fail pretty early on (15-18k miles) and I think I may be headed that direction as well, 20k on the clock. 2018 SQ5.

Still trying to figure out how to diagnose the thermostat.


They symptoms I have experienced 3 times now:

-A/C Luke Cold. Not ice cold, not ambient. Just a bit cool instead of cold.
-Fans running at 100%
-Taking a long time to warm up (oil temp <190* for 20 miles / 40 minutes of driving)
-Coolant Gauge showing 1 tick below middle (where it always seems to be at the middle normally)
-Reduced fuel mileage on the dash (when the symptoms are presenting themselves, like the car thinks it's cold still)


Problem being it has happened totally randomly and I cannot seem to reproduce it on demand. I'm getting no codes and not overheating. Car drives normally, other than the symptoms I listed above. Each time it has cleared itself and been normal after 3-4 restarts.

Another possible piece of the puzzle: It has only happened since I've flashed 034's Stage 1 tune. I have seen 2-3 people say there is a fan issue with the 034 tune on certain box codes. Unfortunately, I cannot find a definitive answer if all these symptoms are indictive of the "fan issue" with the tune or if the thermostat is the cause of the fan issue in my case.

I could flash back to stock and wait for it to happen again, or not happen again, sadly it has happened so randomly already that I have no clue how long it would take to pop up again. Issue I have with this, I've been running the E85 tune and would have to run my current tank down as far as possible and fill with Premium before flashing back to stock. I don't really want to drive the vehicle extendedly if the thermostat is failing. Afraid it will stick closed and leave me stranded somewhere. Stuck open wouldn't be a huge issue, thinking this is what it has done these 3 times already?

Thoughts? Experiences?

[Kondax]

I would quite confidently say I know of at least 20 cars that have had the thermo or water pump fail. All at varying mileage, power, etc.

[STLWIDOWMAKER]

Not to jump on your thread, but wonder how hard it is to replace them ourselves? I remember my B9 A4 being easy enough to get to that I did it myself


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[TheMysticWizard]

Not to jump on your thread, but wonder how hard it is to replace them ourselves? I remember my B9 A4 being easy enough to get to that I did it myself

When first looking at it, seemed decently easy. Then I read that the metal pipe in front of the thermostat has 2 blind bolts where it connects in the rear and also you have to pull the bumper and put the carrier in service position.

I'm contemplating doing it this weekend, but I kind of wanted confirmation that my thermostat is bad before taking on the job.

[tliu91]

2018 s4 45k miles. had 034 stage 1 about 800 miles

Shut engine, check coolant light came on, DTC P000000 with symptom code 33688. Noticed a leak onto the belly pan by the front right wheel.

Otherwise car ran normally, didnt overheat or take long to warm up.

In terms of cost, i got the water pump, thermostat, valve, and gasket for about $300 and getting charged ~$700 in labor for the job in SF bay area

[LongJoap]

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.

I've read a few instances of people having them fail pretty early on (15-18k miles) and I think I may be headed that direction as well, 20k on the clock. 2018 SQ5.

Still trying to figure out how to diagnose the thermostat.


They symptoms I have experienced 3 times now:

-A/C Luke Cold. Not ice cold, not ambient. Just a bit cool instead of cold.
-Fans running at 100%
-Taking a long time to warm up (oil temp <190* for 20 miles / 40 minutes of driving)
-Coolant Gauge showing 1 tick below middle (where it always seems to be at the middle normally)
-Reduced fuel mileage on the dash (when the symptoms are presenting themselves, like the car thinks it's cold still)


Problem being it has happened totally randomly and I cannot seem to reproduce it on demand. I'm getting no codes and not overheating. Car drives normally, other than the symptoms I listed above. Each time it has cleared itself and been normal after 3-4 restarts.

Another possible piece of the puzzle: It has only happened since I've flashed 034's Stage 1 tune. I have seen 2-3 people say there is a fan issue with the 034 tune on certain box codes. Unfortunately, I cannot find a definitive answer if all these symptoms are indictive of the "fan issue" with the tune or if the thermostat is the cause of the fan issue in my case.

I could flash back to stock and wait for it to happen again, or not happen again, sadly it has happened so randomly already that I have no clue how long it would take to pop up again. Issue I have with this, I've been running the E85 tune and would have to run my current tank down as far as possible and fill with Premium before flashing back to stock. I don't really want to drive the vehicle extendedly if the thermostat is failing. Afraid it will stick closed and leave me stranded somewhere. Stuck open wouldn't be a huge issue, thinking this is what it has done these 3 times already?

Thoughts? Experiences?

I had the fans coming on full blast issue supposedly caused by the 034 tune. It had 3 codes with it and after I cleared the codes the car has been fine. I rarely drive it though as I've been driving my summer car so I have no idea if the issue would come back.

[XSWG]

I had the fans coming on full blast issue supposedly caused by the 034 tune. It had 3 codes with it and after I cleared the codes the car has been fine. I rarely drive it though as I've been driving my summer car so I have no idea if the issue would come back.

I don't think it's an "issue" for the 034 tune. They said that they have changed the cooling parameters to account for the potential of higher heat from the increased numbers. Have you reached out to them and provided logs? I think what you're experiencing is normal-ish

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[TheMysticWizard]

I don't think it's an "issue" for the 034 tune. They said that they have changed the cooling parameters to account for the potential of higher heat from the increased numbers. Have you reached out to them and provided logs? I think what you're experiencing is normal-ish

I would imagine the fans would be consistent. I wouldn't expect "normal-ish" would mean that randomly the fans would run 100% from a cold start, then run normally for several weeks only to run 100% from cold start again.

Also from 034 themselves:

As far as the fan issues, I believe we've already spoken about this in the past. Our team has indeed identified this issue on a multitude of customer vehicles, and at this time, we do not have any reason to believe this is harmful or indicative of any engine troubles. We are working on our end to figure out a solution (or a reproducible cause and thus further mechanical support/advice) and likely will be releasing a software update if we can fix this on our end.

I would personally hold off on randomly replacing things, unless you can directly confirm that X part has failed (for example the thermostat and/or AC compressor). As I mentioned before, if this is becoming an annoyance to you, feel free to flash back to stock and the fans *should* go back to completely normal operation.

James Olsen

This was in response to my 2nd email to them when the fan issue happened a third time for me. I have no codes, pending or stored, all 3 times it's happened.

[XSWG]

I would imagine the fans would be consistent. I wouldn't expect "normal-ish" would mean that randomly the fans would run 100% from a cold start, then run normally for several weeks only to run 100% from cold start again.

Also from 034 themselves:



This was in response to my 2nd email to them when the fan issue happened a third time for me. I have no codes, pending or stored, all 3 times it's happened.

I'm not necessarily "a fan" of anyone where I would be biased, my Audis have different tunes depending on the platforms. I just recall them stating previously on one of their live feeds that because they targeted lower Temps that the fans would come on in spurts because of the power loss at Temps over x degrees..

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[TheMysticWizard]

I had written to 034 again, reporting the fan issue and asking if the symptoms I am experiencing are in line with what others experienced.
Their reply went something like this:

As far as the fan issues, I believe we've already spoken about this in the past. Our team has indeed identified this issue on a multitude of customer vehicles, and at this time, we do not have any reason to believe this is harmful or indicative of any engine troubles. We are working on our end to figure out a solution (or a reproducible cause and thus further mechanical support/advice) and likely will be releasing a software update if we can fix this on our end.

I would personally hold off on randomly replacing things, unless you can directly confirm that X part has failed (for example the thermostat and/or AC compressor). As I mentioned before, if this is becoming an annoyance to you, feel free to flash back to stock and the fans *should* go back to completely normal operation.

James Olsen

Based on the advice / info from 034 "we do not have any reason to believe this is harmful or indicative of any engine troubles" I decided to drive the vehicle some more, got it to throw a code now:

15851 - Performance Malfunction in Cooling System
P2181 00 [101]
Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 1
Mileage: 31995 km
Date: 2021.09.03
Time: 15:23:25

Engine RPM: 2134.50 /min
Normed load value: 12.9 %
Vehicle speed: 107 km/h
Coolant temperature: 68 °C
Intake air temperature: 35 °C
Ambient air pressure: 1000 mbar
Voltage terminal 30: 14.180 V
Unlearning counter according OBD: 40
Engine status: COENG_RUNNING
Engine status-Test_Program_Co Eng st COMPU VERB UBYTE: 3

Doing some more research, I stumbled upon information stating that once the coolant hits operating temperature (80-110*C) if it drops below this, it will throw a code (P2181) which is indictive of either the thermostat stuck open or a bad coolant temperature sensor. The reasoning behind this, an engine operating normally will not fall below operating temperature once it reaches it. Further based on the fact the freeze frame shows coolant temperature at 68*C, this makes me believe it is not the coolant temperature sensor, again from what I've read they usually fail way out of range. (From Ross-Tech P2181)

Bottom line, I am pretty confident my thermostat is getting stuck open. I tore into it today got the front bumper and intercooler off, swung the condenser out of the way and verified I can pull the radiator out the front. Tomorrow I will pull the radiator, get the hard coolant line off and replace the thermostat. My biggest worry at this point is refilling the system and getting all the air out. Hopefully that isn't too difficult, I cannot seem to find any such procedure for our engine online.

[tliu91]

I had written to 034 again, reporting the fan issue and asking if the symptoms I am experiencing are in line with what others experienced.
Their reply went something like this:




Based on the advice / info from 034 "we do not have any reason to believe this is harmful or indicative of any engine troubles" I decided to drive the vehicle some more, got it to throw a code now:



Doing some more research, I stumbled upon information stating that once the coolant hits operating temperature (80-110*C) if it drops below this, it will throw a code (P2181) which is indictive of either the thermostat stuck open or a bad coolant temperature sensor. The reasoning behind this, an engine operating normally will not fall below operating temperature once it reaches it. Further based on the fact the freeze frame shows coolant temperature at 68*C, this makes me believe it is not the coolant temperature sensor, again from what I've read they usually fail way out of range. (From Ross-Tech P2181)

Bottom line, I am pretty confident my thermostat is getting stuck open. I tore into it today got the front bumper and intercooler off, swung the condenser out of the way and verified I can pull the radiator out the front. Tomorrow I will pull the radiator, get the hard coolant line off and replace the thermostat. My biggest worry at this point is refilling the system and getting all the air out. Hopefully that isn't too difficult, I cannot seem to find any such procedure for our engine online.

Hope this helps. Also just to note, i installed 034 tune about 800 miles ago and my thermostat is currently getting replaced as well. Cant say i noticed any of the symptoms you had though. car threw code i mentioned above.

Attachment 245831Attachment 245830Attachment 245829Attachment 245828Attachment 245827

[TheMysticWizard]

All that for 3 bolts and a $100 part.

Old thermostat was original (05K17, 5th week? 2017), 06M-121-115-H
New thermostat, (30C20, 30th week? 2020), 06M-121-115-K

I do notice the spring on the end of the newer revision looks to be thicker / heavier. Maybe this resolves a weakness in the earlier part?

Either way, I hope this one lasts more than 20k.

[qcrazy]

Nice pictures! I just hope it fixes your issue. Does the t-stat look open?

As you may be able to tell from the electrical connector, this is not your average thermostat assembly.

[eggraces]

Orange coolant or rusty?

[TheMysticWizard]

Orange coolant or rusty?

Wife asked the same thing. For some reason it looked very orange in the pan. More pink when I poured it in bottle.

[Esmin23]

That’s the color of G13 coolant. Totally normal

[TheMysticWizard]

That’s the color of G13 coolant. Totally normal

Yeah, the new stuff I put in was more vibrant pink, almost violet. The stuff that drained out was more dull with almost an orange shift to it, but definitely still pink, not rusty. Looked it in the drain pan tho.

Hate the feeling of the stuff. Kept getting it on my hands, probably washed my hands 20 times during the job.

[DaveG]

Fully stock B9 S4. Thermostat failed at ~16K miles. Symptoms were full interior fan speed and no control over temp settings.

Replaced by dealer under warranty.

DaveG

[sykokilla]

Having a similar problem with my car now. Threw 2 p2181 codes today around the time I was leaving work. Coolant temps are staying at 68°C(154°F) Outside temp has been a steady 45°F. I have the 034 tune for roughly 300miles now. Will flash back to stock in the morning and see what happens from there.

[skaylesh]

Thermostat progressively failed until it threw an EML at 29000 miles. . Only symptom was radiator fans blowing like a jet engine at all times. I had the thermostat replaced under a third party warranty. Would have cost me £1300 without the warranty.

[robbinsresort]

Having a similar problem with my car now. Threw 2 p2181 codes today around the time I was leaving work. Coolant temps are staying at 68°C(154°F) Outside temp has been a steady 45°F. I have the 034 tune for roughly 300miles now. Will flash back to stock in the morning and see what happens from there.

Any updates?

[gpm24780]

I’m at 29K miles and this just showed up this morning… “Coolant Temperature: Tooo High didn’t have time to stop and scan as I was already on the road… luckily I wasn’t too far away from the Audi dealership… had to pull over a few times to let the whine temps come down but was able to limp over there… the service rep said they’ve had a lot issues with the thermostat and water pumps failing…

[brilliant_black]

Thermostat went at 41k miles on my 2019.

If didn’t fail per say, maybe the seal just failed because I never had any overheating issues.

The car would loose coolant will parked overnight. I could top it off and drive normally.

Replaced it and i haven’t lost a drop of coolant since.

I did buy the extra coolant pipes, o rings, and water pump for the future though since I am tuned and will probably need to do the water pump later on.


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[a4audi4fun]

2017 A4 22,550 km / 13,900 mi. Water pump & thermostat were replaced under factory warranty in July, 2020 prior to me purchasing the car in Feb 2021. Currently at 40,000 km.

[haveyoumetjeff]

Mine made it 60k


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[slws4]

Just chiming in to say that my thermostat started throwing codes as well after tune. Contacted tuner they said it could be that my sensor was already going bad. So ive been just checking the overflow bottle, and topping off when necessary, which i didnt have to do. So recently my car had to go in for other issues, pointed this out to the SA, he took down all the information,and essentially they replaced my thermostat and a host of other things.

[XSWG]

I wonder if this is based on the build date where some thermostats were included. I just cracked 60k miles and have no issue. I've been on jb4 since 8k miles and tuned since ~40k miles.

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[dgraham1284]

I wonder if this is based on the build date where some thermostats were included. I just cracked 60k miles and have no issue. I've been on jb4 since 8k miles and tuned since ~40k miles.

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Same, 2020 S4 , 53,300 miles. Jb4 from 500 miles. EPL tune ~12,000 miles till today.

[slws4]

Same, 2020 S4 , 53,300 miles. Jb4 from 500 miles. EPL tune ~12,000 miles till today.

So car got the t stat fixed. No issues for a week right after tuning (epl); the error came back it’s rather odd.

I know the t stay and some other water stuff was fixed as per tsb. Now with this error I dunno 🤷🏻*♂️

[toxicxk23]

Had the same issue when I first flashed 034 Stage 1 tune. Flashed the updated Rev 2.1 version a few months ago and issue has completely gone away. For my car it looks like it was the tune for sure.

[Tomercohen2]

Did you replace the termostat?that was the problem?or was it the tune?

[Tomercohen2]

Replacing the thermostat solve the problem?

[slws4]

But my WP, TSTAT and software was all redone by audi before going back to EPL stage 2.

Note that i still had the issue after the fact.

I scrubbed the threads and someone on another thread concerning the ea839 engine and tstat, was to unplug the vacuum line that runs to a solenoid check valve. So i did that and plugged it. all errors went away and hasn't came back. I just need to buy a new sensor.

So even if your WP and TSTAT is fine the sensor might be the culprit.

[Tomercohen2]

Audi s4 b9 55,000 km.only in dynamic mode the temp drops from 90c ,vents on full power .replqced the tstat twice,could it be the wtp?
Replaced also al temp sensors…
Or os it the tune(pcp from england)
Please help!!!

[qcrazy]

Take a look at the switching valve.

[Tomercohen2]

Take a look at the switching valve.

The problem is that my car doesnt overheeting,the oppsite,temp guage reading low.
It happends only during driving and fans are working on 100%.
Vcds show p2181.(performance malfunction in cooling system)
It only happen while driving in “dynamic” mode.
If it was the wtp,i think it would happen in every mode no?

[REAPERS6]

I have a 2022 b9.5 s4 1500 miles on it. I have a cooling code and overboost code on the tune this code trips and says “ drive system malfunction “ quick limp mode then runs normal I remove the 034 flash and all symptoms and issues go away. I’m not blaming anyone but the car does not like the tune it’s completely stock just added tune only.


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[AldermanToffee]

97k miles later, I think my thermostat finally bit the bullet.

I’m getting all the same symptoms as OP minus the error code. I am getting two error codes stating implausible signal from coolant temp sensor 3 and cylinder head temp sensor.

I’ve replaced both of those sensors but the issue persists unfortunately.

Very bizarre for the sensors to be causing errors.

[AldermanToffee]

Scrap that, I can’t see it being the thermostat.

The car takes about 30 minute to get to temperature - at this point coolant reads around 70-80c or so.

Once it’s at temperature the fans kick on and the coolant temp immediately drops. I’m guessing at this point it’s thrown a CEL and fans stay on after restarts until I clear the CEL manually.

For reference I’m getting the following 3 CELs:
- Cylinder head coolant temp implausible signal
- Coolant temp sensor 3 implausible signal
- Engine coolant temp too low

So I’m guessing it reaches temp, drops below temp causing it to throw the engine coolant temp too low, which then causes the other 2 CELs to appear.

Despite all this engine outlet and cylinder head temps both read ~90-100c (so normal operating temps). Coolant temp reads 50c~, and I don’t know where the ECU is getting this temp from.

So the car doesn’t even overheat.

[qcrazy]

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?