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ML 270 Fuel Consumption seems odd

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by molloch, Nov 19, 2012.

  1. molloch

    molloch Member

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    Joined:
    Nov 19, 2012
    Location:
    Melbourne, Australia
    Your Mercedes:
    ML 270 2001
    Hi all, we recently purchased a 2001 ML 270 for towing our caravan after reading a number of positive reviews and experiences. It certainly tows the van well, but we took the pair out for a long trip this last week as a test run, and the fuel consumption seemed odd.

    When we first started, the car was doing an average of 13.5 litres/100kms (17.5 mpg) for the first ~100kms. The fuel consumption steadily rose after that (consistently in very similar driving conditions) to 17 l/100kms (14 mpg) over the next 700kms. This was confirmed through working out manually filling the tank, etc. It then remained at 14mpg over the remaining 800kms of our round trip.

    On a flat, straight road, I played around with different speeds and found the fuel consumption as follows (using the on-board fuel consumption read out):

    60kph - 10.5 l/100kms
    70kph- 12.5 l/100kms
    80kph- 15.5 l/100kms
    90kph- 16.5 l/100kms

    This was pretty consistent and it was a fair test, no wind, flat road for around 100kms (central Victoria, Australia), middle of the day in 25 degree Celcius, low humidity.

    I recently drove the car without the van and experienced something similar. I drove around 1500kms, and the first 500kms the car averaged 8.3 l/100kms, (28 mpg) but dropped to 10 l/100 kms (23 mpg) after that for the remainder of the trip.

    Tyres all at 32PSI, car has done 260k, but used no oil, water, etc. Running temp was around 90 degrees C, very consistent.

    Can anyone suggest a possible cause for this? Any home diagnostics I can perform?

    Thanks in advance.
     
    Last edited: Nov 19, 2012
  2. oigle

    oigle Senior Member

    Messages:
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    Joined:
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    Location:
    Redcliffe, Queensland, Australia
    Your Mercedes:
    Currently 2003 ML270. 2012 Nissan Maxima 250SL.
    Firstly, you didn't indicate the size or weight of the van being towed. To give you a comparison, I tow a 16' 1600kg poptop van around the 100kph mark and usually get around 12.5L/100 in good conditions as you describe.
    I would NOT work on figures provided by the onboard computer. They are not reliable. Work on fill to fill with kilometres traveled.
    Your conversion figures are way out too. 8.3L/100 is way better than 28mpg and 10L/100 is way better than 23mpg. Have another go at working them out. As a guide 9.43L/100 is 30mpg. I average about 9.5L/100 in mixed easy driving over a tankful. You might find it easier to work on K's/litre. 10.6kpl =30mpg.
    Are you blowing black smoke under load with the van? You may be suffering from egr problems or jammed swirl flaps. Flaps are easily checked visually for operation. EGR is more difficult to check. It is worth cleaning it thoroughly and installing the egr electronic delete to prevent any problems in that area.
     
    Last edited: Nov 19, 2012
  3. peterwhayward

    peterwhayward Senior Member

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    Joined:
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    Location:
    grays essex
    Your Mercedes:
    E240 classic est 2000 2.4
    Yes 13.5ltrs/100km works out around 21mpg

    and 17ltrs/100km works out around 16.5mpg

    Please excuse my ignorance but I have used GB imperial gallons and not US gallons or anything silly :) (dont know off the top of my head what scale you use in Australia)
     
  4. OP
    molloch

    molloch Member

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    Joined:
    Nov 19, 2012
    Location:
    Melbourne, Australia
    Your Mercedes:
    ML 270 2001
    Bugger, I just typed:

    convert 13.5 l/100kms to mpg

    into Google... Their calculator must be off. It seemed a bit out compared to what I was expecting...but it is usually reliable :)

    The van is a 16ft 1500kg pop-top, it wasn't heavily ladened, No black smoke noticed during the entire trip.

    Thanks for the suggestions thus far.
     
    Last edited: Nov 19, 2012
  5. peterwhayward

    peterwhayward Senior Member

    Messages:
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    Joined:
    Oct 4, 2011
    Location:
    grays essex
    Your Mercedes:
    E240 classic est 2000 2.4
    Thats probably calculated on the U.S gallon.:)
     
  6. oigle

    oigle Senior Member

    Messages:
    3,044
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    Joined:
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    Location:
    Redcliffe, Queensland, Australia
    Your Mercedes:
    Currently 2003 ML270. 2012 Nissan Maxima 250SL.
    Your figures when unloaded are quite OK. Rather poor with van on. No black smoke would indicate that you are not wasting unburnt fuel. No further suggestions unless you want to get your codes read to check all is well generally. EGR delete is still worth doing to prevent future issues.
     

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