VW diesel thermostat / temp control

VW diesel thermostat / temp control

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Alexxtreme

Original Poster:

47 posts

150 months

Wednesday 27th July 2016
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My work horse car is a '11 Passat 2.0l diesel which has sometimes takes up to 40mins plus to heat up on the m/way and other times will be fully up to temp in 10mins... initially I thought it was a thermostat (I have been told this is a bit of a pain to change and includes removal of the alternator), but for the next week it behaves it self! A couple of weeks later, I get the same problem again for a day or so before it reverts to normal.

The question I have is this just a normal VW diesel engine issue and I should I just change the thermostat or is it some other electrical issue and I will need to get my local VW specialist to find the problem / fix it?
I dont want to leave it like this as I expect it will cause damage to the engineering running cold...
Thanks in advance Alex

Edited by Alexxtreme on Thursday 28th July 22:40

Alexxtreme

Original Poster:

47 posts

150 months

Thursday 28th July 2016
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anyone??

powerstroke

10,283 posts

159 months

Friday 29th July 2016
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The thermostat is a mechanical valve that keeps the coolant from circulating though the radiator until it reaches approx 85 c ,sounds like its stuck open , driving slowly there won't be much air flow so the engine will warm up , at speed you will have to much cooling , hence sometimes its ok ... other times takes ages to warm up.....

Alexxtreme

Original Poster:

47 posts

150 months

Friday 29th July 2016
quotequote all
Thanks for the reply... I realise what they do and have had them fail before and stay open.. What I do not understand is the random nature of the heating for the same journey!

xjay1337

15,966 posts

117 months

Monday 1st August 2016
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Alexxtreme said:
My work horse car is a '11 Passat 2.0l diesel which has sometimes takes up to 40mins plus to heat up on the m/way and other times will be fully up to temp in 10mins... initially I thought it was a thermostat (I have been told this is a bit of a pain to change and includes removal of the alternator), but for the next week it behaves it self! A couple of weeks later, I get the same problem again for a day or so before it reverts to normal.

The question I have is this just a normal VW diesel engine issue and I should I just change the thermostat or is it some other electrical issue and I will need to get my local VW specialist to find the problem / fix it?
I dont want to leave it like this as I expect it will cause damage to the engineering running cold...
Thanks in advance Alex

Edited by Alexxtreme on Thursday 28th July 22:40
Hello. I have a Scirocco 2.0 TDI which I will presume has the same engine as yours.

It sounds like the thermostat. However the Alternator doesn't need to be removed but it is not a nice job at all. Also something to bear in mind, I do a lot of my work myself so I have an account with TPS but in this case my tuner who was fitting upgraded fuel pump to my car kindly said he would do it.

I bought the Thermostat without thinking twice but you need to also separately buy thermostat seal which is not included within the thermostat! Stupid eh :-)

90 degrees on the gauge is anywhere between 75 degrees and 105 degrees C temp.
The minute it starts to move off the bottom, it is 51 degrees C

Mine would usually sit at 90 on the gauge but actual coolant temp was between 77 and 82.. fitting new Thermostat it goes up to 89-92 actual coolant temp and stays there. Economy is much better as well.
Sometimes mine would warm up quickly, other times it would take ages.
As long as you buy thermostat from VW or TPS (genuine parts) you will be fine to change just that.

Alexxtreme

Original Poster:

47 posts

150 months

Friday 5th August 2016
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Hi xjay1337, thanks for your comments.... my car is a 11 reg. Is it the same car with the emission VW recall?
Right - had my local garage change the stat - it came as a complete unit including the housing (he said) for around £25. Changing was a right pain for him which including removing the alternator and removing the aircon pipes (needed a re-charge afterwards). £370 in incl the service
So the drive this am was 16 miles with gentle start then 10 miles on the m/way followed by a couple miles and the temp never went above 75C... it even dropped on a down hill section.
I am sure I did not notice this before the same garage changed the timing belt together with the water pump and tensioner. Any other ideas???

xjay1337

15,966 posts

117 months

Friday 5th August 2016
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Genuine thermostat is around £45 from TPS (I get a discount as well) so retail is more like £52-53..

Sounds like a non-genuine unit was fitted. If this is the case, this is probably your issue. Only ever use genuine parts for things like MAFs, thermostats, coolant temperature sensors and the like.

Alexxtreme

Original Poster:

47 posts

150 months

Friday 5th August 2016
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just contacted the garage... it was a genuine item - he was quoting trade price minus VAT.

xjay1337

15,966 posts

117 months

Friday 5th August 2016
quotequote all
Ok - That's good then smile

If that part has been changed and it's still not reading correctly try changing the coolant temperature sensor with a genuine unit.

That being said another check is to idle the engine if it gets up to temp but then cools when moving it's the thermostat 99.999% of the time. It is POSSIBLE that the replacement genuine unit was faulty when installed. Not uncommon.

Alexxtreme

Original Poster:

47 posts

150 months

Friday 5th August 2016
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Thanks... will have a look at the weekend with some further road tests before doing anything else.

R E S T E C P

660 posts

104 months

Friday 9th September 2016
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Just saw this thread. Have you got it fixed yet?

If not... I'm guessing it's got a DSG box?

There's an oil cooler on top of the DSG box. Coolant is fed through this cooler. The problem is an inline thermostatic valve which sits right next to the oil cooler.

It's a common-ish problem, but still bloody hard to find any info about it! I spoke with several VW dealers when I saw people talking about it online, and none of the dealers or specialists had ever even heard of this second thermostat!

This is the part you need: http://www.ebay.co.uk/itm/111951626899
I ordered the same part from that seller for my 2012 Passat 2.0 (140) TDI DSG. I believe it's shared among many/all VAG cars with a DSG box, both petrol and diesel.

It's a really easy fix, although you may want to use a garage to properly drain the coolant and make sure there's no air in the system. I didn't bother draining the coolant, but that risks air bubbles. Also the clips are a bit tricky because of limited space.
15 minute job though... Just remove the air filter box and on top of the DSG unit you'll see coolant pipes feeding in and out. One of them will have a valve that looks like the one in that eBay link. Unclip (couple of spring jubilee clip things), stick new one in... Job done!

After that the car would heat up nice and quick and both oil and coolant temperatures stayed perfect. Also MPG went up, which was a bonus smile

R E S T E C P

660 posts

104 months

Friday 9th September 2016
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This is what you'll see if you remove the air filter box:

Alexxtreme

Original Poster:

47 posts

150 months

Friday 9th September 2016
quotequote all
Brilliant R E S T E C P :-),
I was about to post to say that I have changed the main thermo with still not luck and the problem it seems random. Sometimes it heats up and others it does not. No one I talked to knew of a second thermostat and I had a similar problem on an older BMW 520 where the second thermostat was faulty...
anyway I have brought the stat and will give it a go... the better mpg would be great and it can not do the g/box any good running colder that it should I guess.
Cheers Alex

Alexxtreme

Original Poster:

47 posts

150 months

Friday 9th September 2016
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forgot to mention yes it is a DSG 140 hp model as well (2011)...

Alexxtreme

Original Poster:

47 posts

150 months

Friday 9th September 2016
quotequote all
are you sure this is the correct ebay part.. is says petrol and no mention of DSG etc?

R E S T E C P

660 posts

104 months

Friday 9th September 2016
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Alexxtreme said:
Brilliant R E S T E C P :-),
I was about to post to say that I have changed the main thermo with still not luck and the problem it seems random. Sometimes it heats up and others it does not. No one I talked to knew of a second thermostat and I had a similar problem on an older BMW 520 where the second thermostat was faulty...
anyway I have brought the stat and will give it a go... the better mpg would be great and it can not do the g/box any good running colder that it should I guess.
Cheers Alex
Exactly the same experience I had, very random problem and difficult to demonstrate to a garage because it always worked when I took it in!

If I was doing it again I'd maybe ask a garage to do it for me - the clips can be a bit awkward and I probably did risk letting air into the system. But it's a really quick job so don't let them charge you too much.

Good luck! smile

R E S T E C P

660 posts

104 months

Friday 9th September 2016
quotequote all
Alexxtreme said:
are you sure this is the correct ebay part.. is says petrol and no mention of DSG etc?
100% sure. Same one I ordered. I think they're the same for many VAG cars.

More info here (you need to register to read the thread): http://www.ukpassats.co.uk/phpbb/viewtopic.php?f=8... including mention of part number 1K0121113A which is what you want.

You could try to check with your local VW dealer, but mine had no clue what I was talking about!

Alexxtreme

Original Poster:

47 posts

150 months

Friday 9th September 2016
quotequote all
thanks!

Alexxtreme

Original Poster:

47 posts

150 months

Friday 9th September 2016
quotequote all
and just ordered mine... :-)

xjay1337

15,966 posts

117 months

Saturday 10th September 2016
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Yup the thermostat is kept quiet on the dag box.

Had the same issue in my dsg tfsi.