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Thirsty German...

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Quickbrit, Mar 2, 2009.

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  1. Quickbrit

    Quickbrit Senior Member

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    Your Mercedes:
    2010 E Class 250 CDI Cab
    I had to go to Gatwick this morning, first I filled her up with 95 Ron unleaded 'Tesco special' fuel - because I had a 5p off per litre voucher.

    Ran 70-72 MPH all the way there rarely exceeding 3000RPM, did exactly the same on the way back but had a mad 3 miles of over the speed limit fun - toying with a BMW.

    I used just under half a tank (226.5 miles showing on the clock) filled it back up (39.35 litres) and did the MPG calculation...

    26.2 MPG?

    I've heard people claim 30 MPG from the C280 on a run, is mine normal or do I just have to drive even slower?

    MikeE
     
  2. kth286

    kth286 Senior Member

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    Your Mercedes:
    E320 Coupe 95
    A few weeks ago in my 320 104 straight six just achieved 24% better than that over 220 miles -

    32.5 mpg.

    Two people in car and weekend luggage.

    I was in the economy setting on the gearbox and did not race the engine much.

    I guess it is a blend of driving 'style' and how well the car is maintained.

    Tyre pressures, various sensors been changed, and air filter clean, and spark plugs OK, and correct oil viscosity (use fully synthetic). Esso 95 petrol.
     
  3. jberks

    jberks Senior Member

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    Your Mercedes:
    Jaguar XF 3.0 S, LR Freelander 2, Fiat 500 & Fiat Panda
    mmm - I suspect with a bit of tweaking that could be improved upon.
    Speed does make a massive difference. I've heard tell taht people have achieved 50mpg from an E270. Mine gets tomaybe 42 if I'm lucky and 36 if I press on. Tried it the other day. Set the cruise to 50mph and sat there for 25 miles like a caravanner. 47.6,47.8, 47.9...47.8, never did get to 48. Fat tyres etc all add up.
     
  4. antijam

    antijam Senior Member

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    This is an interesting little graph, produced by the U.S Dept. of Energy

    http://kec.kansas.gov/chart_book/Chapter10/12_SpeedvsFuelConsumption.pdf

    The actual figures are of no particular relevance since I supect they are based on a median american vehicle (and will be quoted in U.S. gallons), however the general shape of the graph shows a rapid increase in specific comsumption as you move beyond 55 mph.

    has any one I wonder checked their consumption when limiting their speed to 55mph (and driving in an appropriately light-footed manner) and then compared that with an everyday consumption - when their speed might rise to a giddy 70 mph?
     
  5. jberks

    jberks Senior Member

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    I did - see above. General motorway driving I never see better than 42.5. Steady 80+ and it's mid to high 30's
    But I can't see why 55 is such a perfect figure. Surely it varies by car, depending on the peak torque output of the engine and appropriate gearing.
     
  6. antijam

    antijam Senior Member

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    I don't think there's anything particularly magic about 55 mph but at high speed most of the engines power is absorbed in overcoming aerodynamic drag, the other mechanical friction losses being very approximately constant.
    Drag is generally considered to be proportional to somewhere between the square and the cube of the speed so it's not surprising that consumption takes a very non-linear dive as the aerodynamic forces become more significant than the mechanical ones.
    Engine torque and gearing are not directly relevant to consumption - torque gives you acceleration, power gives you speed.
     
  7. OP
    Quickbrit

    Quickbrit Senior Member

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    Thanks David,

    What was your typical cruising speed?

    MikeE

     
  8. turbopete

    turbopete Senior Member

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    Your Mercedes:
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    change your fuel would be my advice. i never have been able to get the same power or economy out of ANY of the cars ive owned running on tesco special! in fact none of the supermarket stuff is that great, but if you must use it, morrissons is aat least a decent brand and decent fuel (texaco) unlike the rest! and just as a comparison, my E300 Turbodiesel, with the cruise control set at 70mph, last time i had a long trip, alone, no luggage, returned 39.2mpg!
     
  9. television

    television Always remembered RIP

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    On most cars under 3 liter, there is a break point for the best economy, and that is about 60 mph. as long as the air cleaner is good, there is nothing else one can do.
     
  10. OP
    Quickbrit

    Quickbrit Senior Member

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    As far as car condition is concerned, it's well serviced and with correct tire pressures - the air filter is spotless too.

    The Tesco choice was out of pure convenience (and to impress my Wife with the thrifty coupon usage), I usually run Shell BTW.

    I think you might be right TV, a big motor and a largish chassis is probably not a mix for max MPG anyways (unless you govern your speed).

    MikeE
     
  11. turbopete

    turbopete Senior Member

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    ah yes. keeping the other half happy. not easy! id guess once your back on sell things will improve, even if only slightly! i run mine on shell. that supermarket stuff used to knock 4mpg out of my old 1.6 orion! thats many moons ago, when people could afford to run a car instead of being taxed to death!!!!
     
  12. 5907

    5907 Senior Member

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    I'm getting about 24mpg with mostly urban driving in my W124 E280 estate, using BP ultimate.

    I think it could benefit from a service soon though.
     
  13. st4

    st4 Banned

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    I think you must be right, as the consumption of my car above 60mph does dip quite radically. I notice a 60mph cruise will see 50mpg plus, but 80mph cruise under 40mpg and 90mph mid to early 30's. 100mph + and you're in the 20's :(

    Most cars under 3 litre will have shorter gearing to make up for the relative lack of torque. Hence the lowest speed attainable in the highest gear may be quite a lot lower than a large engined car with tall gearing.

    56mph etc. Old wives tale, its the lowest speed the car can do in its highest gear without juddering etc that yeilds best mph. This is between 45-50mph on my car. On a E350 7g its probably nearer 60 whereas mine would be well and truly above this "optimum speed".
     
  14. Xtractorfan

    Xtractorfan Senior Member

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    I do somehow think that if 30mpg were the norm for a petrol 270 0r 280 then there wouldn't be a diesel taxi in the land, it is possible using the onboard computer to get unrealistic readings from motorway / flat road driving, but all in all a 2.8 petrol engine achieving 25mpg overall is quite respectable..
     
  15. st4

    st4 Banned

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    For an engine designed a decade ago its good. But I had a V8 jeep that @ 60mph would acheive 30mpg. By 70 this was down to mid 20's but 100mph was a good 19mpg. This was a 4.4 litre BMW valvetronic engine. In a saloon car @ 60 I'd reckon 35mpg was attainable from it.
     
  16. Nuclear Bob

    Nuclear Bob Senior Member

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    Haven't noticed much of a difference in economy using tesco or any other outlet. Interestingly tried to see how high the reading got on my C220 CDI sport coupe at a steady 55mph - the answer an amazing 74mpg over 15 miles! I've calculated that the reading is an exaggeration, but only by around 10%, when filling up. Regularly get an indicated 60+ mpg, especially in summer months, on drives of 100 miles or more at standard motorway speeds
     
  17. alindsay81

    alindsay81 Guest

    im getting around 37mpg from my c220 cdi
     
  18. turbopete

    turbopete Senior Member

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    on the subject of fuel consumption, my dads c220 cdi shows around 60mpg (manual 6 speed 'box) o motorway runs at 65 - 70mph. why does this drop by around 10 mpg if its been to dealer and been on STAR for a few weeks then edge its way back to normal?
     
  19. tony2311

    tony2311 Senior Member

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    How does one get 60mph+ while
    alindsay81- im getting around 37mpg from my c220 cdi

    even with different driving style and road can it make that much of a difference?
    i just wirk out my c270 mainly town and short 10mile motorway runs, i get 31mpg
     
  20. JEZ.S320L

    JEZ.S320L Active Senior Members

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    Tried it once on the M4. Gave up after 10 miles or so when my car started to cry :cry:, having been overtaken by an array of Euroboxes.
     

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