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  1. #1
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    Coolant temp sensor

    Can anyone give me detailed intructions preferably with pictures on how to fit a new coolant temp sensor. My temp gauge isn't moving above 70 degrees. I've got an 2000 a4 1.8T quattro sport.
    Thanks peeps

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  3. #2
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    You might need a new thermostat, not complicated to do but its fiddly. You will also need to bleed the system and refill with corect G12 antifreeze mix. You can also change the temp. sensor if you wish but you would have increased fuel consumption and maybe emission lights on dash due to overfueling. Check the colour, if its black you need the new green one, if its blue it might allready been replaced. Hope this helps.
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  4. #3
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    no,

    use the climate control to see what temp the ecu is seeing. that way you know if its the gauge sensor or the stat......

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    How do you do the climate control thing? I don't understand what you mean mate..

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    With the engine running press recycle and up arrow together, 1c should appear on the display then repeatedly press the + underneath until you get 49c on the display and then press recycle again. This will then give you the actual coolant temp.
    Not really sure what this will prove as surely this temp is getting it's info from the same place as the gauge. All it will prove is that the gauge itself isn't faulty, which would be very unusual.
    If the thermostat is stuck open then you should still be able to get the car up to temp by leaving it idling for 15 minutes. Also you'd get more fluctuation in the temp i.e. on the motorway it would drop and in town it would rise. Change the sensor first as it's an easy 15 minute DIY job, but ensure you buy one from a dealer (about 20) and not a cheapo ebay jobbie.
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    My moneys on the 'stat.

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
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  8. #7
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    oh oh 10p wager for me too!!

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    Obviously it could be either, but changing the CTS is soo much easier
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    This cold weather shows up dicky stats a lot more.

    Was driving down the M74/M6 yestarday and noticed that the temp guage wasnt sitting quite at 90. Thaught it unusual so i cracked the laptop out and fired up vagcom. Temp was floating between 78 and 81c. At 81 the guage showed 90, but when it dropped to 78-79 the guage moved slightly left. The stat was replaced about 3 years ago when we baught the car, as it wouldnt heat up at all, but the ambient temp dropped as low as -14c on the journey, and clearly the stat is allowing too much water to bypass the stat and run thru the rad. Running the heating lots as its so cold also robs the engine of heat, further highlighting the effect.

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  11. #10
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    Yes but he's saying his temp never reaches anything above 70 degrees. If it was the stat it would still reach close to 90 when sitting idling, even in the cold weather. When my temp sender went the temp was always between 60-70, it also caused stalling at junctions until the car had completely warmed up, but the symtoms depend on the fault. If it's a decision as to whether it's electronics or mechanics at fault my money's on electronics, can't even remember the last time I had a faulty stat.
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  12. #11
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    I've had two on the 1.8t...
    Matt had one..
    Some other chap had only just changed it and the replacement was faulty...

    In this weather, when your sat with the heating on full bore, a faulty stat could easily stop the temp climbing over 70c even while stationary. He also doesnt say if hes tried getting the engine warm and then leaving it idling with the heating off to see if the temperature climbs to 90c...

    Its a difficult call, and one could surmise that the car could probably benefit from both being changed anyway, but since its only just appeared in the cold weather, if i was asked to choose without seeing the car or running diagnostics, then i'd choose the stat.

    If you want to narrow it down, get the engine hot (ie 10-15mins driving) then park and leave it at idle for 10mins with the heating off. If the guage displays 90 after that, then its almost certainly the stat.

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  13. #12
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    Or just spend 5 minutes changing the CTS first, and see if it solves the problem!
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    Sorry to thread-steal, but I have similar problems still. Temp needle doesn't move from 0 degrees, climate control on auto blows fan on minimum even in the middle of winter (expecting it to be on max tbh) and I am getting on average 18 mpg around town (used to get, I think, up to 24 mpg). Is this likely to be the CTS or the t-stat?


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    What do you get on the CC reading? i.e. obviously the coolant isn't really 0 degrees, so follow the guide above and see what the ECU thinks the temp is.
    Either way I would start with the CTS (obviously) and go from there, it could be both. If it was just the stat then you would just get a low reading as the coolant would be circulating the rad all the time so never getting up to temp unless left to idle for awhile with the heater off.
    Is anybody reading any of this? this issue has been explained over & over and still people seem confused as to how a radiator, thermostat and CTS actually work
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  16. #15
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    Quote Originally Posted by AndyMac View Post
    Is anybody reading any of this? this issue has been explained over & over and still people seem confused as to how a radiator, thermostat and CTS actually work
    LOL - I understand it... I've changed my CTS, but not got around to doing the 'stat yet... it's been too bloody cold! Guage is just hovering above the 60 mark still, so I'm betting once I replace the 'stat everything will be fine. *fingers crossed*
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    Quote Originally Posted by AndyMac View Post
    Or just spend 5 minutes changing the CTS first, and see if it solves the problem!
    or just spend 15 mins diagnosing the problem properly and change JUST the necessary part... youre definately in a world of your own with the suck it and see view

    geeman, before you changed your cts... what diagnosis did you do?

  18. #17
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    Erm... nothing.

    Okay, well not really nothing.

    I checked the hoses, and they were hot.

    My heater is blowing out hot air, which is a good sign.

    My coolant reservoir was weird though... I opened it up while the car was warm... and the water/coolant in there was stone cold!

    Therefore, I thought the 'stat was stuck open.

    But I do have other running problems (cutting out when coming to a stop, lumpy idle, poor MPG) and this all happened after my engine-bay fire. So I'm also swapping out all turbo hoses and putting in a new AFM + connector.
    Last edited by Geeman; 11th January 2010 at 13:33.
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  19. #18
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    i suppose the cts isnt a back breaker of a job, but having a word with the climate control would have saved you the money and effort.

    as for the idle... does your lump have a stepper motor on the throttle body for idle control? it may want a clean (the gum stops the stepper motor from being able to regulate the idle rpoperly)

  20. #19
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    I've just been out for a 'high-speed' run... the ECU was registering no more than 59/60 degrees.

    Had it sat for a few minutes on idle when I came back to see if it rose, and it didn't... still sat at 60, which is what the dash gauge is also showing.

    Money on the stat then!

    For me, changing the CTS was a semi-preventative measure and as it was a simple job, it didn't pain me too much to do it.
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    Quote Originally Posted by Matt82 View Post
    or just spend 15 mins diagnosing the problem properly and change JUST the necessary part... youre definately in a world of your own with the suck it and see view

    geeman, before you changed your cts... what diagnosis did you do?
    that's the point there is no definitive diagnosis, the climate control will tell you the same as the gauge, albeit more accurately. As this is the case then surely it makes sense to anyone with half a brain to do the easier of the two jobs first. Or maybe not.......
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  22. #21
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    Quote Originally Posted by AndyMac View Post
    , the climate control will tell you the same as the gauge, albeit more accurately. As this is the case then surely it makes sense to anyone with half a brain to do the easier of the two jobs first. Or maybe not.......
    wrong. the climate control will tell you what the ecu is seeing, it reports that using a different temp sender.

    so if your cts is bad but your stat is good, the climate control will show 90* and your gauge will show 60-70 etc

    if your cts is good and your stat bad, they will read the same

    so it seems youre the one confused about how half this stuff works

  23. #22
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    So a definite stat change for me then!

    Come on boys... play nice.
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  24. #23
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    its just the bad advice thats given out makes life harder for people..

    anyway, you can thank god youve got a 1.8t, your stat change will be a doddle and all will be well with the world again

    when my stat was duff, i couldnt really give the car beans because the oil would get up to temp and as soon as you went fast the temp would drop

    been tip top since

  25. #24
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    Quote Originally Posted by Matt82 View Post
    wrong. the climate control will tell you what the ecu is seeing, it reports that using a different temp sender.

    so if your cts is bad but your stat is good, the climate control will show 90* and your gauge will show 60-70 etc

    if your cts is good and your stat bad, they will read the same

    so it seems youre the one confused about how half this stuff works
    Oh of course Audi fit a secret secondary temp sender that never goes wrong, just to feed the climate control, I don't think. The CTS feeds the ECU, why on earth would there be another one?
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  26. #25
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    for the temp gauge (G2) and the ecu temp sender (G62) which you can display on the climate control

    ive come across a fair few cars in the past with ecu coolant temp sensors dead, no where near as many with dead senders for the gauge though

  27. #26
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    Ye there are two senders inside the one unit, which is why it has four pins. Two feed the dash, and two feed the ECU. No idea where the climate takes it from though, i'll check the wiring diagram in a bit.

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  28. #27
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    Quote Originally Posted by Matt82 View Post
    for the temp gauge (G2) and the ecu temp sender (G62) which you can display on the climate control

    ive come across a fair few cars in the past with ecu coolant temp sensors dead, no where near as many with dead senders for the gauge though
    Thankyou, G2 & G62 are both in the one CTS, that's why a duff CTS will effect fuel consumption, idling, cold start as well as the reading on the temp gauge. Are we clear now?
    Last edited by AndyMac; 12th January 2010 at 11:11.
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  29. #28
    "Stick a V8 in it!"

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    Its two completely independant sensors, inside one casing.

    So its quite possible that one thermistor could fail, and the other continue working...

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
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  30. #29
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    My coolant temp gauge never fully gets to 90 (normally somewhere between 80-90) despite putting a new thermostat and CTS in. I have just checked the climate and it gets to 90C on there. I'm beggining to think my CTS may be faulty, despite being a new one.

  31. #30
    "Stick a V8 in it!"

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    sounds more like your guage is slightly misaligned?

    Compare it with vagcom readings from the ECU...

    I've had a look at the wiring diagrams, and the climate unit is NOT reporting the ECU temp. The ECU sender only goes to the ECU, the climate control connects to the dash, and gets its data from there.

    So all the climate does is confims the guage is working, if the climate matches the guage the guage is good. The engine side of the CTS could still be faulty.

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  32. #31
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    hi there

    on very late VR6s (mk3 golfs) they combined the two senders into a 4 pin job, which winds people up when the ecu temp sender dies and effectively both ahve to be replaced.

    as for the climate control displaying the gauge... thats bad. you can read the ecu's signal with the measuring blocks on vagcom. that really is important, it controls loads of things to do with performance

  33. #32
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    ^ thats a bit of a weird post matt... Someone else using your PC/Login?

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  34. #33
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    its normal me, hand writing different? ive only been away a couple days :P i did hit the beers pretty hard lastnight though

  35. #34
    "Stick a V8 in it!"

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    well you said "hi there" which seems odd as you've never said that before :P

    You also mention the golf sensor being 4pin as though its a new thing, yet its been mentioned a few times in this thread that the B5 (and everything newer) uses a 4 pin sensor, which is actually two sensors inside one unit...

    Just seemed like someone else had wrote it!

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  36. #35
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    god knows, i didnt wake up feeling very well today and i did enjoy driving the audi to work today. maybe i bumped my head whilst on the beers lastnight too?!

  37. #36
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    A new sender is 20 from Audi, how wound up can anyone get about spending that little cash in a dealership?
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    do you have pics of body kit for b5

  39. #38
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    Only the Votex one some of them had fitted from the factory.
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    stat!
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