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How accurate is your dash computer?

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by MBDevotee, Aug 7, 2012.

How accurate is your fuel computer?

  1. Pretty much spot on.

    34.8%
  2. Well within 1 or 2 mpg

    30.4%
  3. 2-5 mpg out

    13.0%
  4. 5-8mpg out

    17.4%
  5. 8mpg + innacurate

    4.3%
  6. So far out it's worthless

    0 vote(s)
    0.0%
  1. MBDevotee

    MBDevotee Active Senior Members

    Messages:
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    Joined:
    Feb 24, 2009
    Location:
    Yeovil
    Your Mercedes:
    53 270CDI CLK Avantguard + ML500 with LPG
    Just bought a New (to me) CLK.

    Got a few things that need sorting on it - which I'll post in the relevant sections.

    Photos to follow once I have sorted a few minor cosmetics on it (missing wheel badges etc).

    HOWEVER - I have now just used up the first tank of fuel bringing it home and a bit of running around. The fuel consumption on the dash showed the car had done 44.7 mpg from reset until I topped up.

    However working it out, I did 456.7 miles and put in exactly 55 litres of fuel. I brimmed the tank absolutely to the lip at the start and end.

    Now I realise that on one tankful you can't tell too much - however working it out, that makes it just 37.7mpg.

    I'd expect 1 or 2mpg difference - but nearly 20% over-estimate from the dash??? That seems excessive to me.

    I'll keep an eye on it - but just wondered, how accurate are the merc computers for telling you the MPG and other stats?

    Done a poll to see how accurate yours is - please only complete if you actually measure your MPG accurately.

    Thanks
     
  2. turbopete

    turbopete Senior Member

    Messages:
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    Joined:
    Feb 4, 2009
    Location:
    Spennymoor
    Your Mercedes:
    2010 '60' Ford Mondeo 2.0TDCi Zetec (sorry)
    ive found that with my c class, i can fill it to the brim, but it sometimes will drop back so im not convinced the brim to brim method works if taken literally.

    due to unemployment, i have no choice to run my car near empty all the time. i put between £20 and £30 of diesel in per fortnight and travel between 130 and 200 miles approx per fortnight (depending on what i need to use the car for) which makes its lifetime average since ive had the car of 47.something mpg (cant remember the exact figure) as near correct as makes a difference to me. diesel here is 135.9ppl at the moment, which equates to me using around 3-4.5 gallons per fortnight, depending on the runs i need to do.
     
  3. S.Speed

    S.Speed Senior Member

    Messages:
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    Joined:
    Apr 12, 2009
    Location:
    Lancashire
    Your Mercedes:
    Saab 9-3
    On both my C classes the cars computer has been amazingly accurate..
    I would say the pre face lift was slightly more accurate but i am nit picking now..
     
  4. OP
    MBDevotee

    MBDevotee Active Senior Members

    Messages:
    1,367
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    Joined:
    Feb 24, 2009
    Location:
    Yeovil
    Your Mercedes:
    53 270CDI CLK Avantguard + ML500 with LPG
    Mine is consistently lying....

    I am always being told it's hovering around 44 - 44.3 however I am averaging 37 ish (37.3 - 37.5) no-where near 40!
     
  5. rf065

    rf065 Senior Member

    Messages:
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    Joined:
    May 30, 2007
    Location:
    Grossbritannien
    Your Mercedes:
    SLC300 - C250d Estate 4 Matic & Z900rs
    Can you be sure it has not been remapped?

    Mine consistantly gets 1 or 2 MPG more than the dash display states.

    Russ
     
  6. Alex M Grieve

    Alex M Grieve Senior Member

    Messages:
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    Joined:
    Apr 28, 2008
    Location:
    Broom, Warwickshire
    Your Mercedes:
    B Class d200 Sport Premium Plus (66)
    On several cars (C 220 CDI, S 320 CDI, R Class 320 CDI) the trip computer has been correct to <0.5 mpg.

    I keep records of all the fuel I put in, over tens of thousands of miles, so I am confident of the data.

    I see the OBC has a clue to current performance rather than an absolute answer. As you say, you will know better once you have done a couple of thousand miles.
     
  7. juani

    juani New Member

    Messages:
    9
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    Joined:
    May 13, 2012
    Location:
    Tenby west wales
    Your Mercedes:
    c class sport 125 2011 220cdi

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