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Thread: Audi a8 sudden drop in fuel economy

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  1. Audi a8 sudden drop in fuel economy 
    #1
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    Good Evening fellow members, hope you are all having a swell weekend!

    I have a funny one here,

    Having looked at various sites on google and other forum posts this may not be an issue for most but it is doing my head in!

    I have a 2006 Audi A8 D3, it's a 3.0tdi with an Economy map on it

    it sits on around 173k miles.

    The issue I am having is the following:

    1. Cold starts - it chokes quite a bit when starting, may 6-7 seconds before it fires, once it does there is a noticeable amount of smoke from the rear end, blueish blackish in colour. I believe this may an issue with Glowplugs maybe? I thought I would ask here for another opinion.

    2nd and most importantly.

    Over the past 4 years of ownership, any time I would join the motorway the MPG could go over 50mpg with ease, I have managed to reach even 60mpg at one point, this is no BS. 900+ miles out of 1 tank of fuel was easily achieved. Locally it would be around 40+ with ease

    HOWEVER, most recently i have noticed the car struggles to even touch 42mpg on the motorway! Locally it does not go over 30mpg I drove to London from Glasgow and I averaged 42mpg and pretty much the same on the way back. This is including the fact I always used premium diesel (the brand depends on what is more convenient to get to at the time of needing fuel) I managed to get just over 600miles out of a tank. So losing 300 miles surely raises some eye brows!

    Having read other posts I understand that most people would be VERY happy with these figures. However, for me it is a bit of a concern.

    I have read that a terraclean may be a possible solution for this, I have had this done on other vehicles and have been happy with the results but in this case I fear there could be something underlying.

    Any advice offered would be highly appreciated.

    Thank you all!

    Beel.
     
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  2. Re: Audi a8 sudden drop in fuel economy 
    #2
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    Regarding number 1 , glowplugs have nothing to do in this temperature . If we would have temperatures sub zero then yes. You might have issue with supply fuel or issues with injectors.

    Sent from my ONEPLUS A5010 using Tapatalk
     
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  3. Re: Audi a8 sudden drop in fuel economy 
    #3
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    I would get it scanned and see what happening with it. Also do simple checks like cracks in pipes or pipes blown off etc. Could it need a service or the fuel filter is blocked?
    2015 A6 Allroad 3.0TDi 218 CRTE - NEW
    2012 A6 Avant 3.0TDi Multitronic - OLD
     
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  4. Re: Audi a8 sudden drop in fuel economy 
    #4
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    Is it as quick as usual to warm up?
    Does the temp sit at 90˚c on a cold day, at all speeds?
    There is a inline coolant regulator beside the auto box on the 3.0 tdi and it fails open and coolant is no longer regulated by the thermostat and wastes fuel and gives poor heater output- common fault.
    Audi A8 - 2015 - 3.0TDI
     
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  5. Re: Audi a8 sudden drop in fuel economy 
    #5
    Join Date
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    Is it using oil?
    Current- A6 C8 40 tdi quattro s line Daytona Grey
    Gone-S3 sportback, A6 C7 biturbo saloon,A4 B 8.5 avant, A6 C6 3.0 tdi Quattro saloon, A6 C5 2.8 Q Avant
     
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