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Temp Guage not working - coolant temp sensor changed... now what?

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by car4kids, Dec 12, 2010.

  1. car4kids
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    car4kids New Member

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    [Dec 12, 2010]
    I've had an issue with the temp guage ever since I got the car. It is the 2.5tdi... I have changed the temp sensor but wondering if there is anything else I should try.

    Guage typically doesn't move at all (reads a low temp) very occasionally it seems to rise to 50 to 55 deg C.

    Would it be possible to test the sensor / guage by dipping the sensor in my coffee with the ignition turned on? I could then see if the guage and sensor are working and move on to working out why the coolant is below temperature (thermostat?)

    Any help much appreciated.
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  3. car4kids
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    car4kids New Member

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    [Dec 12, 2010]
    Just tried dipping the temp sensor in a cup of coffee. The sensor and guage are working! I got a reading of 90 deg C from water straight from kettle into a cold cup - so probably about right...

    So I can assume that the coolant in the vehicle isn't reaching temperature. Why would this be? is there a device that controls the flow of coolant or a fan that I should be checking?
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  4. paul20v
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    paul20v Audi fanatic

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    [Dec 12, 2010]
    Thermostat i would change next no question .
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  5. Fahim
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    Fahim Member

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    [Dec 12, 2010]
    Thermostats stuck open continually allowing coolant through the engine.

    Replace it and you should be good to go.
    #4
  6. stu_m
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    stu_m Active Member VCDS Map User

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    [Dec 12, 2010]
    before replacing the stat check your heating if your stat is stuck open you wont have no heating if you have heating it WILL be the sensor regardless of it saying it works in your coffee!!

    mine was playing up if left running it would eventually read 90 but as soon as i started driving it dropped straight back down
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  7. paul20v
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    paul20v Audi fanatic

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    [Dec 12, 2010]
    You will have heating as the heater matrix heats first even before the thermostat ,
    it may not be so good but it will work well
    but leaving it high idle to build up temp as said then drive to see what happens .
    #6
  8. stu_m
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    stu_m Active Member VCDS Map User

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    [Dec 12, 2010]
    i thought the heater matrix was in with the engine circuit and the stat keeps the engine circuit at around 90 degrees so warms up with the engine and with a stuck stat you will just have the full circuit open and the rad will just cool the coolant just as quick as it can heat up so will get very little heat if any!
    #7
  9. swarcup
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    swarcup Well-Known Member

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    [Dec 13, 2010]
    100% thermostat, every single 2.5 driver goes through the same questions and always end up changing the stat and it cures it.The stats always fail in the open position, it will give you heat through the vents. Expect the front end off and while you have that off its good practice to swap the water pump,cambelt and tensioners, and the other belts aswell, then the diesel pump will require retiming with vag-com. Expect to pay around £600 mark. Not bad for a £30 part eh
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  10. paul20v
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    paul20v Audi fanatic

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    [Dec 13, 2010]
    heater matrix is 100% nothing todo with the thermostat side of things it gets fed direct from the engine independent of the main cooling circuit ,
    for eg if the thermostat stuck closed the heater matrix would still get hot .
    #9
  11. car4kids
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    car4kids New Member

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    [Dec 14, 2010]
    Cheers everyone... the stat is getting changed as I type. I'm more a cheque book owner than a box of tools owner - every five minute job I turn my hand to takes a week due to inexperience.

    The unfortunate thing here is that the timing belt was changed by a VW dealer just a few days ago... I did ask them to sort the temp guage issue at the same time. They handed the car back to me with the temp guage not working telling me it simply needed calibrating and only Audi could do that for me.

    So I am left to foot the bill once more for the front end to come off and have the thermostat replaced.

    The coffee routine truely works. If you dip the temp sensor in a hot coffee then you do get a true indication of whether the temp guage / sensor is at fault or not. I never saw the guage read anything above 60 deg C and straight away it read correct at 90 Deg C so I am certain the coolant never dot up to temp.
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  12. stu_m
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    stu_m Active Member VCDS Map User

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    [Dec 15, 2010]
    yeah i understand what your saying coolant goes round the engine first then to heater matrix back round to the stat area and if the stat is open it will go to the rad then feed back to engine if stat is closed then it just goes straight back to the engine until up to running temp

    what i mean is say after 20 - 30 mins driving the heater will still not be as hot as it should be if the stat is stuck open as the engine will not get to operating temp it will just be over cooled the coolant will prob be luke warm in this weather
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  13. A4tdishane
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    A4tdishane Member

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    [Jan 31, 2012]
    Hi guys I've replaced the sensor and the stat on my 1.9 tdi yet the gauge just does its own thing still
    Could my dash be at fault if so is the a DIY repair ??
    Thanks
    #12
  14. pauldazzle
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    pauldazzle Active Member

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    [Feb 1, 2012]
    Did you use a genuine VAG temp sensor?
    #13
  15. A4tdishane
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    A4tdishane Member

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    [Feb 1, 2012]
    Yeah got it from vw dealers
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  16. swarcup
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    swarcup Well-Known Member

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    [Feb 1, 2012]
    i replaced my temp guage in my pod, its quite easy, only thing is you cant buy them seperately from audi. Best thing to do is to buy a donor pod from ebay and swap them over. B6 and B7 needles differ slightly so try and get a b6 pod. also it may be worth checking what wiring you can see prior to doing this
    #15
  17. bowen
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    bowen Member

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    [Feb 1, 2012]
    I have the same problem.

    Temp gauge intermitently works, sometimes reaches 90 other times 60 or it doesnt move at all. I replaced the temp sensor twice as sensors can be bought faulty. Again no joy.

    One day i just sat in the car after a run, turned the engine off and on again i repeated this four maybe five times. The needle would rise to 90 then as i turned the engine off the needle would flicker or stutter. One time i tried this i turned the ignition off, removed the key and the needle was still sat at 90!?

    Im putting this down to a faulty temp pod now? anyone else have any idea?
    #16
  18. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Feb 1, 2012]
    Im saying this too, it dont matter how you try to sugar coat it lads, the truth always goes back to the Thurmostat, I had this on my 2.5TDI and iv seen it on 3 others since i joined this forum,

    It is a cam belt off job, so you may as well change it, new water pump too and a new thurmostat, like it or lump it, this is the truth.
    #17
  19. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Feb 1, 2012]
    the pods do go mate, try swapping it over and see if that fixes it, i have a pod if your close to Northampton you can try it with,
    #18
  20. bowen
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    bowen Member

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    [Feb 2, 2012]
    Thanks for the offer mate, but if your ever on a weekend break in South Wales let me know. Would i just be able to buy a second hand set of clocks pop out the temp gauge pod and swop with my duff one?
    #19
  21. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Feb 2, 2012]
    i may be able to sell you a 2nd hand set of clocks and Cargo them over to you ?
    #20
  22. A4tdishane
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    A4tdishane Member

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    [Feb 2, 2012]
    Pm you :)
    #21
  23. sherbet31
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    sherbet31 New Member

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    [Feb 2, 2012]
    Hi,
    i have a 2003 tdi 130bhp and am having probs with the temp gauge/coolant temp. I have replaced the thermostat and the temp sensor (both with genuine VW/audi parts from dealer) but the gauge seems to struggle maintaining at 90 degrees. I can drive the car and eventually it will climb to 90 degrees but if i stop to idle(traffic lights, traffic etc) the gauge slowly drops down to 70 degrees. Also if i stop the engine and restart within say 10 minutes the gauge again will have dropped to 70 degrees. I have had a look at the viscous fan but it does seem to spin freely, it does have a slight resistance after the engine has been run for about 15 minutes. Is this normal?
    Its a real head banger and am running out of ideas?

    HELP


    Regards
    Sherbet31
    #22

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