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Coolant Temp sensor - TDi

Discussion in 'A3/S3 Forum (8L Chassis)' started by sprout99, Aug 28, 2007.

  1. sprout99
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    sprout99 Member

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    not sure if we've done this before.

    My temp gauge is not reading right. So i guess the temp sensor on the block is playing up. Do you agree?

    However, where is the offending item and how much are they?

    Any info would help

    Thanks
    Ian
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  2. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    £20 from the dealer, not sure exactly where it is on the TDi but usually at the back of the engine, will be situated in the top hose, with an electrical connector plugged into it either blue or green. Unplug the connector, remove the circlip holding the sensor in and it'll pull out. Release any pressure in the system first by taking off the cap on the expansion bottle, but remember to put the cap back on otherwise the contents will syphon out of the system when you remove the sensor.
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  3. sprout99
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    sprout99 Member

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    apparently it's a 4 pin one?

    plugs into thermo housing (27quid!)
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  4. Tooks
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    Tooks Member

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    When you say it's not reading right, what do you mean?

    Is it just all over the place, not moving at all, or struggling to move above 70c?

    Have you compared it to the temp reported by the climate control, if fitted?

    Reason I ask is that I suspected the temp sensor, but on mine it was the thermostat. The symptom was that it struggled to get above the min mark on the gauge, but the reported temp via the climate control was 90c+.
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  5. sprout99
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    sprout99 Member

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    thats it exactly.

    a few weeks ago it took ages to move and i thought nothing of it.

    this morning it struggled to move above 65 / 70

    i've bought a thermostat - 27 quid !!

    it fits into top of a 3 way pipe? please tell me this is correct?
    Thanks
    Ian

    p.s how do you check through climate
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  6. Tooks
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    Tooks Member

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    With the ignition on, press and hold the recirculation button. Then press the manual flow control up arrow. You should see a 1c. Press the temperature up ("+") or down ("-") buttons to select a channel number. Once you've selected a channel, press the recirculation button again to display the value.

    Channel number 49 is the one you're interested in, it's the digital temp from the coolant sensor.

    The coolant thermostat on my TDI engine is on the front left of the block as you look at it from the front of the car, very near the alternator.

    What engine code do you have, I can check my workshop manual?
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  7. QUATTRO_REP
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    QUATTRO_REP Diesel Power!

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    i have this problem, but my temp gauge is a bit all over the shop, sometimes it'll work and display a steady 90, but then it will drop all of a sudden to the min. the digital readout is the same. is this an easy job to do? been buggin me for a while just not got round to looking at it.
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  8. Tooks
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    Tooks Member

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    Very straightforward to do.

    Remove the undertray

    Drain the old coolant from the drain point bottom nearside of the car

    Remove the bolts holding the coolant pipe that has the theromostat behind it

    Replace the thermostat and pipe

    Tighten up the coolant drain point

    Mix the fresh coolant (from the dealer or specialist) with water to the desired ratio shown on the bottle and refill the system.

    Run the engine until hot, and check the levels

    The official workshop procedure mentions removing the alternator, but I found this wasn't necessary on my PD130 engine.

    Quattro Rep, what sensor reading are you comparing it to?

    Channel 51 is the adjusted temp, which isn't really a reading, and channel 49 is the actual temp sensor reading.

    I think the gauge and the digital temp sensor take their feed from the same point, so with my thermostat problem, the open thermostat just never allowed the water to heat up properly, and the gauge and sensor matched.

    A gauge that read different to the sensor would most likely be a faulty gauge or dashpod problem I'd have thought.

    With yours being so erratic, and if the sensor reading and gauge are jumping around in unison, then I would suspect the temp sensor giving erratic readings..?
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  9. sprout99
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    sprout99 Member

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    mines an ASZ 130 pd

    i noticed heater was working ok this morning as i had cranked it up. i checked this when i noticed gauge was doing a dance between 60 and 70deg c

    i'll try sender and worry if that doesn't fix problem
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  10. QUATTRO_REP
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    QUATTRO_REP Diesel Power!

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    my heater works fine and engine seems to heat up as normal, just the readings on the dash is a bit weird now and again....mostly all the time now, it can show anything between 0 and 90...but never over. cabin always warms up, just thinkin this needs to be sorted b4 the cold weather starts. ive got a ASZ 130 as well.

    i'll check 49 on the way home tonight.
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  11. sprout99
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    sprout99 Member

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    i'll let you know what happens tonight after trying new sender / sensor

    i noticed mine playing up a while ago but it hadn't bothered me until today

    Tooks, how much is thermstat? just in case
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  12. Tooks
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    Tooks Member

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    Can't remember exactly how much, but it wasn't much more than £20, and that was from the dealer.

    Let me know how you get on.
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  13. sprout99
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    sprout99 Member

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    changed the sender and after refilling coolant all is ok

    i spent more time looking for the little fooker than the time taken to remove and refit.

    it's down situated at the back of the engine on the lower hose. just above the gearbox.

    been for test drive and fuel fill up. all seems well.

    Thanks for the advice boys.

    Ian
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  14. QUATTRO_REP
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    QUATTRO_REP Diesel Power!

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    is the thing accessable from the top, or did you have to get down under the car? how much coolent did u loose? gonna do this at weekend i think.
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  15. sprout99
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    sprout99 Member

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    i'll take a photo

    i lost about 1.5 litres
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  16. sprout99
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    sprout99 Member

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    as promised.

    [​IMG]

    this is the location of the pipe


    [​IMG]

    this is where the sensor is - it is up the rear :salute:
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  17. QUATTRO_REP
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    QUATTRO_REP Diesel Power!

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    fark, id have never have found that! cheers mate! i had it in my head it was round the other side...very helpfull :applaus:cheers!:icon_thumright:
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  18. Philios
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    Philios New Member

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    Not sure if anyone is still looking at this post but here we go.
    I've got a similar problem with my A4 TDI, temp seem to struggle to get up to 80. But the biggest problem is the heater coils don't work unless I unplug the temp sensor. (Its the sensor at the back of the engine(Think it's temp sensor?)) Its like the cold temp is set warm so thinks it doesn't need to use heater coils.
    I was told by the guy I bought if off that he had already fitted a new sensor but it still did the same thing.
    Can you get to what temp its set at using the aircon control display?

    :think:
    Phil
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  19. mayurw
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    mayurw New Member

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    hello

    mine 2001 has developed a smillar problem, the gauge had been jumping between 60 - 90 but before that it would stick at 90. I have changed the sensor mentioned and now it fails to even move, occasionally it will work and stay at 90. Now I have used the AC controls to read the 49 and 51 reading and I'm confused. 49 reads 30oC all the time and 51 went up from something low to 75oC, does this mean I have a thermostat problem ?
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  20. Philios
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    Philios New Member

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    How do you look at the settings using the Aircon display?
    Also this give me another headache because the aircon display don't work that good. It flickers and goes off all the time. Is this just a loose wire of easy fix?
    My car sounds like a bag of spanners but it was cheap as chips and sort of works....
    #20

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