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  1. 3.0 tdi cooling problem 
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    Hi all, I have a 3.0 tdi 2006 A8 with a few problems which I think are all related to cooling.

    First problem is that the temp needle does not get to 90 degrees, ever. Just come back from a 3hr run, and it hit roughly 70deg. (possibly thermostat)

    Second problem, in the cold, it takes a really long time to start up. I have to crank the engine for a while, longer than my old a8 to get it started. No matter what the temperature the glowplug light only comes on for less than one second. I did a service on it last month, and one of the fault codes was glowplugs 1 and 4 were open, and indeed they were. They were replaced. No difference to starting, or any other of the issues. (possibly coolant temp sensor)

    Lastly, mpg is not as good as it used to be, prob because the engine is running a bit cold.

    So my is it the temp sensor? or is it the thermostat? could it be both?

    I did read somewhere that if you disconnect the temp sensor, the glowplug light should come on for 20seconds. I wanted to try that, but I couldnt find the sensor location!!

    I cant even find the thermostat!

    admittedly, I havent looked under the car. I was thinking I may have to take the bumper off.

    So does anyone know where those two items are?

    Any suggestions on the problems? or should I just replace the two parts.

    Many thanks in advance.
     
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  2. #2
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    I would change the sensor first.

    Sent from my GT-I9100 using Tapatalk
    A4 2.5 tdi QS (mapped)


     
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  3. Re: 3.0 tdi cooling problem 
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    I have had the same problem (your first problem) since I bought mine 6 months ago.
    I don't have the glow plug/cranking issue though.
    Your first problem, I could have written your description myself, in fact, here's a post I made earlier (post 18#)...

    http://forum.a8parts.co.uk/showthread.php?t=2809&page=2

    As you see, I have replaced two genuine thermostats and two CTSs to no avail.

    The CTS is under pipe after the Airflow meter in the back corner of the engine.
    Access just needs the removal of the large diameter air piper via the jubilee clips.

    The thermostat is at the front of the engine near the top, you can see it with a torch, it has a 2-3" rubber pipe coming off it.
    It's a bit of a fiddle to undo the pipe's spring clip, not to drop the screws and to wiggle it in without breaking it, as space is cramped.
    You can see a CGI of the engine here...
    http://www.youtube.com/watch?v=mbjzUMCBf2Q



    If you want thermostat and CTS parts, I have some you can have for postage cost. Only fitted a fortnight at most.

    I am looking at coolant bypassing the thermostat now.
    Some of the pipes contain one-way valves and chokes.
    eg, there is a short small diameter corner pipe near the back of the drivers headlight, if you feel this there is something hard inside in the middle. There are also some big pipes under the engine, so I want to remove the belly pan and give these a squeeze too.
    Audi A8L- 2006 - 3.0TDI
     
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  4. Re: 3.0 tdi cooling problem 
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    Hi Snapdragon!

    First of all, thank you so much for your help!

    so the first thing I did was to drive the car without the AC on.... and that worked, the car stayed at 90 degrees.

    then I found the temp sensor, under the MAF, took it out, and tested it. at about 100degrees it was reading 300ohms, at 0degrees, it was reading about 6kohms. does this sound about right? Seems as though the sensor is working.

    Then to check the electrics I put a variable resistor onto where the sensor usually goes, as I lowered the resistance the temp needle inside went up until it got high enough for the cooling fan to spin at super speed! So that circuity seems all ok.

    How difficult is it to take the thermostat out? I think that will be the next job now, but going from what you have told me, and the fact that when the AC is off, the car temp is fine, it might not be needed. It must be the cooling fan then, doing some silly thing, or the thermostat is a little bit stuck.

    I think some more driving at speed needs to be done with the AC on and off, to see what happens. Will report back!

    And thank you for the offer of the stat and sender, might have to take you up on it if there is a problem, but hopefully we can get to the bottom of this.

    Before I forget, I have an x431 scan tool which gives me almost the same functionality as vcds... and group 7 gives me 4 temperature readouts. I know the last one is the coolant temp, but what are the rest?

    maybe these engines just run a bit cool, or there is a problem with the 2006 model somewhere...
     
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  5. Re: 3.0 tdi cooling problem 
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    after another run, this is what happened..

    AC off. The car warmed up in about 10mins to 90, then at 15min the car started cooling down to 70ish, and never got back up to temp.

    sounds like thermostat to me... I think I'll change it... can't send you a pm snapdragon,

    could you send me your email please.. cheers.
     
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  6. Re: 3.0 tdi cooling problem 
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    Hello guv.
    Yours sounds like mine.
    There is coolant going into the radiator (or too much coolant).

    I too measured the OHMS of the CTS and found a difference between the old and new, at various temps, but this didn't seem to make a difference, maybe it was the tarnished metal giving contact resistance on my crocodile clips.

    Replacing the thermostat is not hard and doesn't lose too much coolant. I just let it pour out and rinsed it off.
    I used Comma G40 which is the correct type.

    It is mounted in a plastic housing with an outlet pipe. It is a single assembly and the whole thing is to be replaced.
    It is held on with 4 or 5 10mm hex head screws.
    A mirror on a stick and a torch is useful for seeing the screw heads.
    There is a poly-v belt running across the bottom which can be push down with a hammer handle or similar when you come to withdraw or refit the thermostat.
    I can email the instructions anyway.


    Any of these things can make mine run cool:
    Driving in cold weather
    A/C on when not really needed.
    Cruising at higher speeds >30mph for any period.
    Idling

    I have noticed that if I do hit 90˚c, which is always in hot weather and heavy traffic, doing any of the above
    will bring the temp down quickly.

    I have noticed that the cooling fans seem set to run when stood still. They start soon after stopping, so if I open the bonnet and stop and jump out and run to the front they are not turning and about a second later, they start up.
    I initially thought they were running all the time until I caught them off for the first time.
    I don't see how the fans are the culprit as over 40mph-50mph or so, they aren't really useful as ram-air effect takes over and this is when mine can cool down to about 55-60˚c.
    Last edited by snapdragon; 02-05-2018 at 09:01 AM.
    Audi A8L- 2006 - 3.0TDI
     
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  7. Fuse box wiring diagram 
    #7
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    Does anyone have a fuse box wiring diagram for a 2004 Audi a3 1.6 auto petrol.?
    Any help would be much apprichiated
     
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  8. Re: 3.0 tdi cooling problem 
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    Hi,

    Not an expert in this particular area but I have had prior experience with a BMW 330d with issues along these lines. In case it helps your thinking:

    If the cooling fans are running when they shouldn't be, it might be worth checking all of the aircon sensors as well - I recall that there are about half a dozen things that can set an electronic cooling fan off, including: coolant temp, aircon refrigerant temp, aircon refrigerant pressure, speed sensors, and so on. I think they are also variable in their speed settings as well which would suggest a resister-controller type arrangement (akin to the HVAC 'hedgehog').

    My BM experience was of electric aux cooling fans running at full crack all the time when was at low vehicle speeds, When going faster they would turn off and, for example, when slowing for a roundabout, you could hear them cut back in. Engine temperature gauge never varied from normal however. Turned out to be a defective aircon pressure sensor that was tripping the fans on all the time.

    Sounds to me like there might be a combination of one or more rogue sensors causing cooling fans to do inappropriate things (hence correlation with aircon usage) and the thermostat not adjusting to the excessive cooling that is resulting from duff sensors?

    Question therefore: can you find out the definitive list of all things that can 'call' the electronic cooling fans? You can then go through each one to test as it may be a 'peculiar' one that you wouldn't ordinarily expect that is causing the issue.

    All the best

    E
     
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  9. Re: 3.0 tdi cooling problem 
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    For anyone finding this, it was the coolant regulator mounted beside the gearbox 4E0121113. It is an inline thermostat made of black plastic and was failed open allowing coolant to flow continuously through the gearbox cooler and main radiator.
    Audi A8L- 2006 - 3.0TDI
     
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  10. Re: 3.0 tdi cooling problem 
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    Good to hear that you sorted this out.

    I had similar problem, but in my case the faulty was Aux Heater (as weird it sounds it's true xD). When it was running the temperature gauge was showing up to 70 and then was dropping something all way to the left. Spend 3 days trying to sort it out and after reading everything about thermostat and temperature sensors I got to the video suggesting that Webasto may have be the cause. Even with trying all the possible coding I couldn't get it to work properly, so at the end I just turned it off. And so far temperature is 90 while driving. Need to check how it will be under 10 degrees but so far it's not that cold here .
     
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