MK6 2010 Passat B7 TDI running cold - Please help

Discussion in 'VW Mk6 Golf, Jetta, Beetle, Sportwagen TDI forum' started by bentas1, Jun 30, 2016.

  1. bentas1

    bentas1 New Member

    Joined:
    Jun 30, 2016
    Messages:
    4
    Car:
    VW Passat 3C 125TDI 2010
    Location:
    Victoria Australia
    Hi,

    I'm looking for some assistance in trying to diagnose my 2010 B7 3C 125TDI CFGB engine Passat which is running cold.

    Initially I suspected the thermostat because even after an hour running along the freeway, the temperature would float around 50-60c (outside temperature between 5-15c). When in heavy traffic, the temperature might get close to 90c but would generally fall way once on the move again. I also confirmed these temperatures using vagcom and compared the 2 temperature sensors which rose in temperature together (also indicating a faulty thermostat).

    I then went out and bought a new genuine VW thermostat (with housing) and spend the best part of a day installing it.

    Unfortunately I'm still getting the low temperatures and the car is not reaching operating temperature with both sensors still rising together.

    In further testing this morning I ran the car for about 20 minutes parked in the driveway at 2000 RPM, the car did reach 90c with the radiator feeling hot at about 50c (which makes me suspect the new thermostat was also opening early). However, I then went for a light (flat road) drive and expected the temperature to fall away which would have confirmed a faulty thermostat, though it did not (and would not) and stayed at the correct temperature of 90c.

    I've established the following:

    - Temperature sensors appear to be indicting correct values (also confirmed against similar oil temperatures).
    - Thermostat has been replaced with Genuine VW one.
    - Radiator does warm up at the same rate indicating thermostat is faulty.
    - Car's temperature does not drop away once 90 has been reached during light driving, indicating nothing wrong with thermostat.
    - If car has not reached 90c before driving, it will never reach it during usual driving conditions and will rise and fall based on driving conditions.

    Does anyone have any ideas as I'm really confused about what to do, or test next and I don't really want to purchase another thermostat at $120 on suspicion the new one might again be faulty?

    Would it be possible the heat is being incorrectly circulated with pump 2 (diagram 8 below) ?

    To me, it's a complicated network of pipes which I don't properly understand.

    Thanks for assistance in advance. :)

    Regards,

    Ben




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  2. xeno555

    xeno555 Well-Known Member

    Joined:
    Dec 12, 2011
    Messages:
    1,643
    Car:
    2012 TDI Tech Package 6mt
    Location:
    Mile High
    Mods:
    Malone Stage II. Rawtek 3" from Turbo to Tail. Slammed on Koni. TSW Nurmburg Rims. Whiteline Sway & Ends. Panzer Plate.
    bubble in coolant system?
     
  3. bentas1

    bentas1 New Member

    Joined:
    Jun 30, 2016
    Messages:
    4
    Car:
    VW Passat 3C 125TDI 2010
    Location:
    Victoria Australia
    No, no bubbling or anything out of the ordinary, coolant is also retaining its pink colour.
     
  4. rexb

    rexb New Member

    Joined:
    Sep 10, 2016
    Messages:
    2
    Car:
    VW Passat 125tdi wagon 2012
    Location:
    Victoria
    Ben,
    I am interested to know if you got to the bottom of this problem. I have exactly the same symptoms with our 2012 125 TDI Passat. I am convinced it is a stuck-open thermostat, but the local VW dealer says there is nothing wrong and they've never heard of another Passat with a similar issue.

    So now I am going to replace the thermostat myself. Do you have any advice on the best way to go about it? I can't find anything about the model and "how to" get the thermostat off with minimum effort on the web.
     
  5. bentas1

    bentas1 New Member

    Joined:
    Jun 30, 2016
    Messages:
    4
    Car:
    VW Passat 3C 125TDI 2010
    Location:
    Victoria Australia
    Hi,

    No, unfortunately I have not got to the bottom of the problem. As stated up the top I initially relaced the thermostat and on the first drive the temperature went straight to 90 and I assumed I'd fixed the issue. The next day the same issue returned.

    On investigation of the removed thermostat I found it was opening about 75c instead of 88c though I think this was only part of the problem.

    After a month I proceeded to relace the new thermostat assuming this was faulty with another new one. Unfortunately the issue didn't resolve and upon testing the removed thermostat I found it was working correctly.

    My attention then turned to the (secondary) electric EGR coolant recirculation pump (as I believe this is used to quickly warm the engine using the exhaust gasses) and I also replaced this is as it was worn and not running smoothly. This also has not corrected the issue.

    Interestingly, each time I refill the coolant system the car preforms perfectly (but only until it is turned off and re-started) which suggests the computer is doing something strange? (maybe something to do with anti pollution system valve not letting exhaust gasses through resulting in less heating of the coolant.)

    As I'm not a professional with the anti pollution system or computer system and can only find little information on this issue I plan to take it to VW in the coming weeks to see if they can locate the issue.

    FYI: replacing the thermostat is a pretty long and tedious job and can take up to 8 hours by the time you remove the battery etc, intercooler pipes, pull back the water pipes and remove the thermostat. (you'll need patience, lots of lights, small hands and some universals to get around corners & an allen key with a round end for the thermostat)

    I'd be interested to her how you go.
     
  6. Bryan W

    Bryan W New Member

    Joined:
    Oct 2, 2016
    Messages:
    2
    Car:
    VW Passat TDI 2011
    Location:
    Perth WA
    Changed thermostat, my problem is the same as yours! fine one day doesn't get warm the next,interested to hear if you ever fixed it?
     
  7. bentas1

    bentas1 New Member

    Joined:
    Jun 30, 2016
    Messages:
    4
    Car:
    VW Passat 3C 125TDI 2010
    Location:
    Victoria Australia
    Hi,

    Yes, still having the same issue. I took the car to a German car expert a few weeks ago and they charged me a couple of hundred dollars to tell me they thought it was the thermostat (despite me changing twice and testing the second one which I removed)

    When the car is started from cold the radiator will warm before the temperature gauge gets to 50c, however the heat doesn't appear to be coming through the thermostat but rather from the electric circulation pump which pulls heat from the EGR cooler. I'm pretty sure this is the root of the problem (either the pump running when it shouldn't or not enough heat from the EGR cooler maybe because of a valve)

    I'd be interested to hear any progress you make on your car.

    Regards,

    Ben
     
  8. Bryan W

    Bryan W New Member

    Joined:
    Oct 2, 2016
    Messages:
    2
    Car:
    VW Passat TDI 2011
    Location:
    Perth WA
    Will do Ben!
     
  9. Cuspurs

    Cuspurs New Member

    Joined:
    Jan 10, 2017
    Messages:
    1
    Car:
    Volkswagen Passat B7 2.0 TDI 140 Variant 2011
    Location:
    Latvia
    Ben,

    I am having a similar issue.
    If the temperature drops sub-zero (C), the problems start.
    In city mode driving agressively the temperature rises. As soon as I go above 50kmh or leave the city and hit the highway, the temperature drops, feet are freezing and all in all it is a terrible experience.
    Changed 2 thermostats, since VW dealer confirmed that the first one was faulty (happens 1/100).

    Long story short.
    1. Brand new thermostat.
    2. In city, slow speed, traffic - temperature goes till 90°C.
    3. As soon as I go faster and consume less fuel, the temperature needle hits the ground.

    Really looking forward on what could be the issue.
     

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