2011 B7 2.0 TDI Passat Overcooling issue, Need advise.

[kimken]

Hi all,

I need your advice.

The car is 2011 B7 Passat 2.0 TDI(140) DSG and mileage is about 110k miles.

Few weeks ago, when the weather gets cold down to 0 degree, I noticed coolant temperature went down to 60 degree whilst cruising on A-Road or motor way. The gauge was solidly pointing 90 degree before this happens for more than one year since I got this car. I am a cabbie so the car has been used whole year constantly and there was no issue in the winter last year.

When the temperature gauge goes down, the hot air temperature also goes down correspondingly.

So I first doubted the thermostat and replaced with a genuine thermostat from TPS but no luck.

Then I replaced coolant temperature sensor on the engine, again with a genuine parts from TPS. When I take out the old sensor, it's anodised gold surface was peeled off. So it was an obvious issue on the sensor. Since replaced this sensor, I felt some improvement as the gauge stays on 90 most of the time but sometime still temperature goes down to 70 degree on cruising(even outside temperature is 9 degree...) but recovers to 90 soon after stuck in traffic. However, the weather has not get that cold since I replace the sensor, it may have not been improved.

Then I changed another coolant temperature sensor located on the hose, which I believe to deal with radiator fan. But no luck.

Can anyone have any thought on the cause of this issue and advise if anywhere else I need to check on it?

Thanks in advance.

kimken

[Crasher]

This is a version specific issue, DSG models have two thermostats and some have three, some manuals have two and not others. The additional thermostats are in line from the EGR cooler to the oil cooler and to the trans fluid cooler. There is a VW Technical Product Information notice about this problem which basically states there is nothing that can be done about it, the engine is just too efficient, I quote "the lower limit of the operating temperature of 70°c may only be slightly exceeded" and basically infers that you should turn off the cabin heater and next time you order a car, specify the auxiliary heating system PR- 9M9. Your car should have the electric auxiliary heater PR-7E6 and pre June 2011 build versions were very prone to going wrong so a fault code read of the HVAC system would be a good starting point.

[kimken]

Hi Crasher,

Thank you for very helpful information. I appreciate and respect your activity in this forum!

My car is registered on 20/06/2011, so it seems like a pre June 2011 build version....

I will bring the car to mechanic tomorrow to deal with a suspension issue, so I will ask them to see if any fault code on the HVAC system and also check whether the car has third thermostat or not.

With regard to the auxiliary heaters, my understanding is that the PR- 9M9 is an external heater to warm up coolant when needed and PR-7E6 is an external heater to add warm hot air when the coolant temperature has gone down. Is this correct?

I will also contact VW customer support and check my car has those auxiliary heaters or not.

With regard to the "VW Technical Product Information notice" you mentioned, where can I access those information? Do I need to subscribe "erWin"? or local dealer can provide me if requested?

Thanks,

kimken

[Crasher]

The TPI's are classified but sometimes they leak out. I can check your cars build spec from your reg number so PM it to me and your email.

[kimken]

Thanks.

[kimken]

Hi Crasher,

I tried to send you message but I am not able to send as I have not posted 15 messages yet... My reg is LO11BXM and email is vwaf@jst-9.com.

Thanks again for your help.

kimken

[Crasher]

I received your PM, I have sent you an email.

Interestingly, the TPI in question has been removed from the system, I had to get it off my archived copy.

Your car is “PR-9M0 Without auxiliary/parking heater” and has the “PR-7E6 Electric auxiliary air heater”

[kimken]

Hi Crasher,

I received the email, thanks again.

We located the second inline thermostat today and replaced it.

Will see this cures the problem and let you know.

Regards,

kimken

[kimken]

Hi Crasher,

The issue has now been resolved. Coolant temperature and Oil temperature are now stable as before.

I appreciate very much for your input, thanks again.

Reagrds,

kimken



Regards,

kimken

[Crasher]

So was it the second thermostat or the one to the DSG cooler?