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Thermostat or Temp sensor??

Discussion in 'A3/S3 Forum (8L Chassis)' started by finesse, Mar 5, 2010.

  1. finesse
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    finesse Active Member VCDS Map User

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    [Mar 5, 2010]
    Hi chaps,

    Having a temp gauge issue, I have searched the forums but the symptoms for both a similar so not sure. Currently would like to get one of either...

    • Temp stays at 80 deg on motorways
    • Takes a while to warm up to 70 then 80
    • When I briefly stop or turn of engine, after restart the temp sits on 90 for a few minutes but then returns to 70 or 80, depending on how hard am driving

    Any ideas fellas?

    Thanks
    #1
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  3. FactionOne
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    FactionOne Well-Known Member

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    [Mar 5, 2010]
    When you kill the ignition and then re-start the engine quickly after, what does the fan do?

    //R
    #2
  4. finesse
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    finesse Active Member VCDS Map User

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    [Mar 5, 2010]
    Thanks for your reply FactionOne,

    I do not know if the fan starts up, I will have to open up and get back to you thanks.

    If it starts or does not start, what does it mean?

    Thanks
    #3
  5. FactionOne
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    FactionOne Well-Known Member

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    [Mar 5, 2010]
    Well, from the symptoms you described I was leaning towards the stat - I'd have probably thought sender (as everyone knows they're about as reliable as a two bob watch <ducks>) until you mentioned that you get 90° on the dash briefly after a quick kill and re-start. From my own experience and others' I've read about it's quite rare for a busted sender to ever offer 90°; so that kinda made me lean towards the sender having it right but the stat kicking the fan in erroneously and it bringing the temp back down again. I could imagine soak from a hot engine bringing what was 80° coolant back up to 90° pretty quickly (which might explain why you see it briefly on re-start). Of course it's mainly conjecture until we know what the fan's up to.

    ...Oh, and having said that, I might be completely off-track - If it was a computer or a television audience measurement instrument I'd be certain, but my overalls still have L-plates on them. As I say, it seems plausible going off past experience though...

    Let us know what the fan's on with...

    Regards,

    Rob.
    #4
  6. finesse
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    finesse Active Member VCDS Map User

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    [Mar 5, 2010]
    Really appreciate your help Rob!!


    Thanks will let you know what the fans do.

    Just to throw in another insight, on the motorway today, I exited and entered a petrol station. I did not stop but just drove through (no RON 98 available). The temp guage went up to 90degs, but droped again after I started driving.

    Strange
    #5
  7. jonny87
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    jonny87 Active Member

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    [Mar 6, 2010]
    mate my advice to you and to anyone else who has similar issues is to replace both sender and stat, sender is 5 min job and costs no more than £10, stat is bit trickier but do able, take 1-2hours cost again no more than £10 and you will need replacement coolant (audi g12 £7 a ltr)

    jobs a good 'un :icon_thumright:

    if i had to choose id say your thermostat is kaput, mine was the same when i bought it, but as above i would do both
    #6
  8. finesse
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    finesse Active Member VCDS Map User

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    [Mar 6, 2010]
    Thanks Jonny
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  9. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Mar 6, 2010]
    Its 90% the stat, the CTS tends to make for poor cold starting or a dead needle IME
    #8
  10. jonny87
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    jonny87 Active Member

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    [Mar 6, 2010]
    :thumbsup:
    #9
  11. random101
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    random101 Member

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    [Mar 6, 2010]
    I have the exact same problem...
    Let me know what you think it is
    #10
  12. finesse
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    finesse Active Member VCDS Map User

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    [Mar 6, 2010]
    Than fans only start after I switch off and on, when I turn on the heating
    #11
  13. FactionOne
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    FactionOne Well-Known Member

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    [Mar 6, 2010]
    Hmmmm, that's not quite as conclusive as I was hoping for, but yeah - if I had to go and buy only one of the two parts, it'd be the thermostat (it relieves me that by thinking has some parity with Byzan's - he's a VAG black-belt); although as above if you can spare the extra couple of quid it might be worth buying both, as that leaves you with a further three options:

    1) Change the stat and if that doesn't fix it, change the sender and then relax in the knowledge that they're both nice and fresh.
    2) Change the stat and if it does fix it, get your tenner (or whatever they are this week) back on the sender
    3) Change the stat and if it does fix it, stick the sender in a drawer somewhere nice and safe for when it does (almost inevitably) fail.

    All the best,

    Rob.
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  14. finesse
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    finesse Active Member VCDS Map User

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    [Mar 6, 2010]
    Thank! I will get thermostat asap.

    best quote for genuine

    thermostat + seal £21.57
    temp sensor + o £29.18
    #13
  15. martin g
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    martin g [censored]

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    [Mar 6, 2010]
    I have a similar issue, only mine never gets to 90, flicks between 60 and 80, ive bought a sender and am confident it will fix the problem. Car drives fine just has the EML on.
    #14
  16. kelk11
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    kelk11 Member

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    [Mar 6, 2010]
    since having my cambelt and water pump changed the temp was fluctuating from 90 to 87 ish, changed the thermostat and now it ranges from 90 to 80...any ideas?? as mentioned it all came about after cambelt and water pump being changed

    also changed the temp sender a while back as needle was dropping to 60 and back up to 90 which solved that problem so i know its not related to that.

    thanks
    #15
  17. jonny87
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    jonny87 Active Member

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    [Mar 6, 2010]
    i didnt use gen audi stuff, went to my local motor factors, stat was a fiver, sender was £7ish, been on the car for 5 months no worries
    get 2 bottles of gen audi g12 coolant as i said in previous post think they are 6-7 quid a bottle
    #16
  18. Welly
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    Welly VX220 SC Driver :)

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    [Mar 7, 2010]
    Same for me as above. Stat was £3.20 from a motor factors and I got my sender from ebay.

    All good.

    Always worth doing them both - then you know they're both good.

    Happy days....:icon_thumright:
    #17
  19. A3Tom
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    A3Tom Smell my finger.

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    [Mar 7, 2010]
    GSF or Euro will get you all the parts and coolant you need for about £35 tops all in :)
    #18
  20. finesse
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    finesse Active Member VCDS Map User

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    [Mar 7, 2010]
    Cool, will check out GSF.

    Went for a drive around town, noticed;

    The temp stays at 90 when interior heating/fan is switched off

    When the heating/fan is switched on the temp drops to 70-80


    I guess the thermostat is the issue.
    #19
  21. finesse
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    finesse Active Member VCDS Map User

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    [Apr 16, 2010]
    Thanks Byzan, Faction

    First changed the sender but no change. Finally changed the stat today, works like a dream.

    Warms up so quick
    Engine feels silky smooth
    Fan blowing really hot
    Temp gauge glued on 90

    :D


    Thanks again
    #20
  22. 1animal1
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    1animal1 The Clar!! it mouves!!! VCDS Map User

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    [Apr 16, 2010]
    ow much fun was it fitting :)
    #21
  23. finesse
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    finesse Active Member VCDS Map User

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    [Apr 16, 2010]
    Did it the long way round, alternator off, charge pipe moved

    lol

    Not fun, but worth it
    #22
  24. 1animal1
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    1animal1 The Clar!! it mouves!!! VCDS Map User

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    [Apr 16, 2010]
    yeah i found it good to put several nice dollops of grease on the seal to hold it in place whilst you replace the cover.... mine kept falling off everytime i tipped the plastic pipe upside down :)
    #23
  25. Matt82
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    Matt82 Active Member

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    [Apr 16, 2010]
    my money says stat. how would a cts know how to react to the car being on the move or not etc
    #24
  26. 1.8tplym
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    1.8tplym Member

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    [Apr 16, 2010]
    Sorry Guys,

    About to sound really daft question after all the above. Should i expexct my temp gauge to sit at 90c all the time no matter what conditions outside are? My car only hits 90 if its a hot day, i have run her for 10 mins and i have the interiior fan on lo (not with the air con on) It sat between 70 - 80 today on my way to work but that was a 06.00 this morning with the outside temp around 3.0. if so i guess i need stat and sender change too?
    #25
  27. 1animal1
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    1animal1 The Clar!! it mouves!!! VCDS Map User

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    [Apr 16, 2010]
    most likely thermo but as said you might aswell change both..... defo a problem as should sit on 90 no matter what
    #26
  28. 1.8tplym
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    1.8tplym Member

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    [Apr 16, 2010]
    Thanks Animal,

    So what will the dodgy stat do to the car? any serious damage? i have heard it will eat my mpg. Anything else i should worry about?
    #27
  29. sekenzo
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    sekenzo Member

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    [Apr 16, 2010]
    it should be the stat. Had exactly the same problem with mine 2 months ago. Replaced the stat and it now stays spot on in 90. Its a relatively easy DIY job. Took me about 1 hour. Will be slightly easier if you have small hands :o.k:

    I experianced get poor milege and rough idle with a faulty stat.
    #28
  30. finesse
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    finesse Active Member VCDS Map User

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    [Apr 16, 2010]
    Stat and O ring 24quid from Audi.

    Change the stat, best thing you could do,
    #29
  31. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Apr 16, 2010]
    Stat stuck open will take longer for engine to get up to temp, if ever, so will eat a few extra MPG's.
    #30

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