Help Please How to diagnose a faulty thermostat with VCDS?

jakm15

Registered User
Is there a way to dertermine if my thermostats are faulty with VCDS? My temperate guage never rises to 90 unless I'm really pushing the engine, after many hours researching various sites I've found a lot of conflicting advice to weather this is normal not.

I've found the parts that I need and they are only £38 for them both but it's the time I don't want the waste changing them if they are not faulty.

I've monitored the coolant temperature when driving and it gets to around 75C when doing about 85mph, at normal round town driving it's about 68. My engine is a 140 CAGA 2.0tdi mapped to 180.
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Mike B

Registered User
Impossible cos the stat is a simple device non electrical .Yours has almost certainly failed open.A good way to check is to see if the heater works well and early
 

jakm15

Registered User
Impossible cos the stat is a simple device non electrical .Yours has almost certainly failed open.A good way to check is to see if the heater works well and early
Yeah the heater works well and warms up probably after 5 to 10 minutes of driving.

In regards to the stats being non electrical I was wondering if there was more than one temperature sensor, say for example before and after the stats, I could then monitor these and if they both rise the same I would know the stat is faulty whereas if one sensor gets to 82 and the other is still at ambient I would know it's not at fault. I'm not sure how many places you can monitor the temp and how.

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Mike B

Registered User
I don't know if yours has 2 but my 2.5tdi B6 has only 1 and I have never heard of an engine with 2 and cant see why there would be.If your heater is good then it might be the CTS which you can check.Mine always gets to 90 quickly and stays there with a heater as good as any but I believe some diesels are not so good in cold weather
 

jakm15

Registered User
This is the stat that my car has, I've checked on elsawin and on the car as well.

I monitored the coolant temperature yesterday at idle and the radiator output temperature and the both were rising from cold start. I'm not sure if the stat should be preventing water from flowing through the rad at cold start or not but it currently is flowing.

The stat is only £28 so I'm going to change it in the next few months when I've got some spare time and I'm feeling patent.

I'll report back then what the score is as it may help others as I've seen dozens of threads like mine with no conclusion.

Cheers.
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Mike B

Registered User
Does sound like the stat.The rad should not warm early and maybe the stat is leaking too soon .They can weaken with age.Change it and you might get even more heater power and better mpg
 

Cerbera9

Registered User
The temperature gauge in the instrument cluster is only a guide and not very accurate, it will only move is there is a big change in temp. Very much like the oil temp goes up and down according to the conditions the water temp does the same if you monitor it through VCDS you can see this but the instrument temp gauge will stay rock steady at 90 indicating normal operating conditions.
 

AudiLeon

Well-Known Member
VCDS Map User
The guage iirc is set to show 90 even when its below and above to stop people worrying. So if it's that low. It may be even lower. Just change the stat. Easy enough and you know it's done. Genuine only i suggest.
 

jakm15

Registered User
The temperature gauge in the instrument cluster is only a guide and not very accurate, it will only move is there is a big change in temp. Very much like the oil temp goes up and down according to the conditions the water temp does the same if you monitor it through VCDS you can see this but the instrument temp gauge will stay rock steady at 90 indicating normal operating conditions.
That's what all the previous cars/vans I've had are like but this one seems to differ to the rest, I've monitored the coolant temperature on VCDS and the guage on the dash follows this measurement very accurate. Once it gets to 52 the guage starts to move then and follows the VCDS reading very close, only goes to 90 if that is what what VCDS shows and drops also if it does.

Thermostat change is planned so I'll see if that makes a difference.

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Muharrem Tumcakir

Registered User
That's what all the previous cars/vans I've had are like but this one seems to differ to the rest, I've monitored the coolant temperature on VCDS and the guage on the dash follows this measurement very accurate. Once it gets to 52 the guage starts to move then and follows the VCDS reading very close, only goes to 90 if that is what what VCDS shows and drops also if it does.

Thermostat change is planned so I'll see if that makes a difference.

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Hello,
I have been living with this known problem on my B8 A4. The service checked my exhaust system fault warning and stated that thermostat is moving earlier. They suggested to change whole pump since the thermostat could not be changed seperately! The cost is around 300 €! I have not researched whether there is another solution or not, just decided to live on with it. Is there a safe and cheaper way to change only thermostat of my A4 B8 (U.S. Version with 6-speed)?


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Jon B

Registered User
The Audi 2.0 TDI system is a peculiar beast when it comes to temp.

Even the manual says it is normal in cooler operating conditions for the needle not to set at 90.

That’s said my TDIe 136hp will always get to 90 eventually - especially above 60mph. But I’ve never had a car that takes so long to get up to temp.

My local Audi specialist says it’s normal and to be fair, the car runs apparently as it should.
 

Mike B

Registered User
I have heard that some diesels will not get right to 90 when its cold outside but it doesn't seem right for the needle to drop back like this.Cant believe the pump has to be changed with a stat.I would get another opinion
 

Muharrem Tumcakir

Registered User
I have heard that some diesels will not get right to 90 when its cold outside but it doesn't seem right for the needle to drop back like this.Cant believe the pump has to be changed with a stat.I would get another opinion

Yes definitely the situation needs another opinion. The exhaust system fault led on the instrument cluster is still bright for the new logical alternatives.


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xmgcx

Registered User
Hi Jakm15,

I have the same issue with my A4, did you get around to replacing the thermostat and did it resolve the underheating issue ?

Thanks
Mark



This is the stat that my car has, I've checked on elsawin and on the car as well.

I monitored the coolant temperature yesterday at idle and the radiator output temperature and the both were rising from cold start. I'm not sure if the stat should be preventing water from flowing through the rad at cold start or not but it currently is flowing.

The stat is only £28 so I'm going to change it in the next few months when I've got some spare time and I'm feeling patent.

I'll report back then what the score is as it may help others as I've seen dozens of threads like mine with no conclusion.

Cheers.
6d7204952453377e02bbabd753dea87b.jpg


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xmgcx

Registered User
Based on your reply I changed mine yesterday, been for a couple of test drives and its fully resolved the issue.
Looking at your posts mine was exact same thermostat and I also found vcds was showing a temperature that matched the dash gauge, both were pretty much always low around 70 degs max.
This was on a A4 cab 2008 2.0 tfsi.

Thanks.
 
Last edited:

audiwaterpump

Registered User
Is there a way to dertermine if my thermostats are faulty with VCDS? My temperate guage never rises to 90 unless I'm really pushing the engine, after many hours researching various sites I've found a lot of conflicting advice to weather this is normal not.

I've found the parts that I need and they are only £38 for them both but it's the time I don't want the waste changing them if they are not faulty.

I've monitored the coolant temperature when driving and it gets to around 75C when doing about 85mph, at normal round town driving it's about 68. My engine is a 140 CAGA 2.0tdi mapped to 180.
735510105a3f5dbe2fc2307971890f02.jpg


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If you have a cap on your radiator, try changing that as it can affect the pressure in the system, and the pressure can affect the temperature of the coolant.
 

jakm15

Registered User
Based on your reply I changed mine yesterday, been for a couple of test drives and its fully resolved the issue.
Looking at your posts mine was exact same thermostat and I also found vcds was showing a temperature that matched the dash gauge, both were pretty much always low around 70 degs max.
This was on a A4 cab 2008 2.0 tfsi.

Thanks.
That's great I'm glad it's sorted your temperature problem out, maybe you'll get a few more miles to the gallon now as well.

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audiwaterpump

Registered User
That's great I'm glad it's sorted your temperature problem out, maybe you'll get a few more miles to the gallon now as well.

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What was the mileage and age when you had to replace the thermostat?
Thanks
 

audiwaterpump

Registered User
The Audi 2.0 TDI system is a peculiar beast when it comes to temp.

Even the manual says it is normal in cooler operating conditions for the needle not to set at 90.

That’s said my TDIe 136hp will always get to 90 eventually - especially above 60mph. But I’ve never had a car that takes so long to get up to temp.

My local Audi specialist says it’s normal and to be fair, the car runs apparently as it should.
If the amount of heat leaving (heater, radiator, cold outside, dodgy stat, etc) the cooling system is greater than the amount of heat entering (driving style) the cooling system then it will never reach 90.
 
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