B7 temp issue

[Darks RS]

hi all! Hoping someone can assist.
Recently I noticed that the wife's B7 TDi wagons temp gauge was doing a wobbly i.e. Going to normal then reducing with the increased airflow ie at 80+ then I noticed that it was taking a long time to warm up at all.

Took it to a specialist here in the ACT , he hooked it up to VCDS but there were no codes, but he did notice that coolant temp was about 80ish

He advised thermostat, so replaced it but sure enough it started doing it again.. $480 poorer but still frustrated anyone have ideas what it could be?

[Umai Naa!!]

I've replaced one on an Octavia Scout recently, which I believe uses the same style of thermostat.

Was definitely stuck open.

I don't envy the guy who has to do it again, because they're not the most straight-forward of jobs.

[Darks RS]

But could it be a dud thermostat or something else ? Temp sensor?

[Umai Naa!!]

Possibly both. Could depend on the brand of thermostat, too. The one I fitted was a Meyle, which believe it or not, was a genuine VAG one with some of the markings melted off. I have seen a few other brands around, which aren't necessarily known for their quality.

The gauge isn't terribly accurate, too. It'll it the 'normal' 90degC, while actual coolant temp is still around 50degC.

Might be worth having your preferred mechanic put his diagnostic computer on it, to get a true-er temp reading from the ECU itself, or even just put a temp probe in the expansion bottle. Both those readings are within a few degC of eachother. Also, the fans cut in at around 95degC.

[Darks RS]

Ok replaced thermostat and both temp sensors, no fault codes and live Ecuador data sometimes has readings of -40c???

Specialist is stumped. What next?

I've noticed that oil temp also doesn't like rising too and will also go up and down.

[Lasa911]

This is an Old topic; however, someone would find it this information is Useful.

There is a known problem in Passat B7 Diesel Vehicles where Coolant temperature does fluctuate as you drive the vehicle.

I have had this problem after 3yrs of purchasing the vehicle. To explain the problem, vehicle is not reaching operating temperature quickly enough or temperature drop when you are on a freeway. Since I have taken the vehicle to dealer and it was repaired under Extended warranty. Since then the same problem have re-surfaced again after roughly about 3yrs since it was repaired. Currently I’m out of Extended warranty and dealer wants around $550-600 to fix the problem.

I have done a bit of Google research.

Findings referred to a secondary thermostat valve call “Coolant regulator” located near DSG oil cooler and this does cause the problems when its jammed open. (not reaching operating temperature quickly or temperature drop when you are on freeway)

I have referred to my original repair invoice and found out, it was the same Coolant regulator was replaced in last repair and its showing exact same symptoms for second time around.



Forum Link, Click Here

So, I have followed some instruction from a forum, where explain that how to remove the valve and found out it was the same valve AGAIN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!

This time in fact, it was jammed open as well. With closer inspection with dismantling the valve, I have discovered; it was due to dried coolant residual deposits inside the piston chamber of the thermostat.

You can’t get this valve from VW local dealer as they are selling the whole assembly including tubes along with valves for around $230, Or


1- Buy this Coolant regulator on eBay for about 20-30 Euros. (This opens at 75 Celsius). Part Number is
1K0121113A

2- Try to dismantle the valve and clean the piston and cylinder assembly with alcohol & WD40. (without damaging the rubber sleeves inside the thermostat or the piston-pin). Notes—if you are pulling the pin out of Thermostat, do not use your pliers more than 2mm from the end of the pin or you will damage the surface of the pin, don’t push any thin in to the thermostat cylinder will scratch the surface inside.



After repair the valve, you could check it by holding with pliers and placing in hot water, it should push out at around 75 Celsius and should retract when run under tap water.

BTW – I don’t know for how long? will this last

[Umai Naa!!]

I'm not convinced this would have any great bearing on the engine coolant temperature. DSG temperature, sure.

The main thermostat would cause a bigger difference in temperature compared to this.

[Lasa911]

Hi Umai Naa,

I could confirm that after stuffing around with DSG thermostat, its been working fine for last 2 months. (BTW-it was the second time I had this problem in my Vehicle)
my Temperature drop issue is fixed and Temp gauge does not drop below 90 degrees any more when I'm travelling on the freeway.

Initial Problem

[sportpaket]

Hi Lasa911,

Many thanks for the information in this thread. I have been suffering this problem for approx 2 years and have discussed it with both a VW dealer and a couple of other European specialists. None of them could give me a definite answer as to whether I needed a new main thermostat or just the DSG thermostat. Prices quoted were very high too.

Based on your experience & the link provided, I ordered the DSG thermostat on eBay from England (just under $70 delivered) and installed it quite easily today in under an hour. The old thermostat was stuck open as expected.

Took it for a short drive & the problem is finally fixed! The engine reaches & maintains 90 degrees quickly once more & I couldn't be happier. Thanks for taking the time to share your knowledge on the subject, it saved me a significant amount of money & helped me fix a problem that was very frustrating. Hopefully others will benefit too!

[Darks RS]

Apologies in the end it was the DSG thermostat. Took it to the dealer and it was replaced and all the issues went away. Specialists in the ACT didn’t know but I told them both about it after. VW knew exactly what the issue was and advised that quite a few 2012 B7s had the same issue so much that they had the part in stock.