***deteriorating mpg recently***

Discussion in 'Engine' started by SHAKTER, Dec 22, 2010.

  1. SHAKTER

    SHAKTER Hardcore MB Enthusiast

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    Hi all,

    Recently I've noticed a slight fall in fuel economy in my w124 300CE. Is it normal for this to happen in the cold weather? I have been flooring it, but only a little. Heaters are usually on full heat.

    Also, I seem to have a slight voltage fluctuation too. I've noticed that the interior/exterior lights glow stronger and also heater vents blow stronger upon acceleration but when coming to a halt (in 'D'), everything get noticeably weaker. Sometimes to the point where the engine cuts out and stalls.

    Any advice appreciated.

    Thanks! :thumb:
     
  2. OP
    OP
    SHAKTER

    SHAKTER Hardcore MB Enthusiast

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    Oh and I normally average about 18mpg around town - not really pushing it. That sounds low to me - any thoughts?

    Thanks again.
     
  3. lxi

    lxi Hardcore MB Enthusiast

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    You have probably been driving not only with heater on full blast but rear screen heater on, headlights on, heated seats (if you have them) on - all these things take a bit of power each so combined, quite a load - all of which affect consumption.

    Cold weather does affect batteries so the alternator is working hard to try to keep up, hence flickering dash
     
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  4. Bellow

    Bellow Hardcore MB Enthusiast

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    Isn't that typically Diesel, and partly due to the winter formulation?
    I've been surprised that my petrol engine has delivered its best MPG returns in 48,000 miles - and that despite the temp gauge dropping during driving the weather being so cold. I put it down to very slow processions on A-roads and using the big gears and very little throttle on the Bs, which have been treacherously slippy with snow and ice.
    Turbo petrols seem to thrive on low ambient temps - it even sounds more purposeful!
     
  5. Charles Morgan

    Charles Morgan MB Club Veteran

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    My W124 E320 has been burning a bit more, which isn't surprising given the much increased load. My round town mpg isn't that different.
     
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  6. wemorgan

    wemorgan MB Club Veteran

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    My diesel is 20% less efficient than a few weeks ago.
     
  7. lxi

    lxi Hardcore MB Enthusiast

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    cold air is more dense that hot, so there's more oxygen in each "breath" the car takes which gives better consumption & performance
     
  8. tali

    tali Hardcore MB Enthusiast

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    I 've had 18 mpg from numerous 4 cylinder cars under 2 litre -just by constant urban driving:crazy:
    Winter weather (for me) has had no effect ever on reducing MPG -in fact nothing else has either
     
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  9. BillyW124

    BillyW124 Hardcore MB Enthusiast

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    how many miles would you typically get out of a full tank? do you have a 55 lit tank?

    ive had issues with low mpg and had recently got my car serviced and throttlebody cleaned. ive managed to churn out 298 miles @ 56liters my light for refill has just come on. the math wotks out to be 24 MPG (combined)

    its strange as i used to get only 220 miles out of a tank! i am pleased though. Going to fill up again and see what happens this time round (i did put redex in to my full tank too) not sure if this has helped but i was being very econmical on this tank.
     
    Last edited: Dec 22, 2010
  10. renault12ts

    renault12ts MB Club Veteran

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    I got my best a couple of weeks ago because of the cold and snow...51.7mpg at 50mph over 120 miles.
     
  11. BillyW124

    BillyW124 Hardcore MB Enthusiast

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    apologies for the spelling erros above!
     
  12. gIzzE

    gIzzE MB Club Veteran

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    Cold will always use more, up to around 20% more. However, the conditions often mean you also drive a fair bit slower so you can end up getting better MPG, but drive a car at 25ºc and again at 2ºc in the same way and you will get worse MPG.

    Diesels can use up to 40% more fuel before getting up to temperature and when it is cold it can take 10 miles or 15 minutes to get there, hence why people doing short journeys in the cold can see a real hit in consumption.
     
  13. OP
    OP
    SHAKTER

    SHAKTER Hardcore MB Enthusiast

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    Thanks Billy. I usually average about 18mpg, which to me still seems low. Not sure what the total tank capacity is actually. Haven't filled up a full tank in a while - don't drive much unfortunately :(
     
  14. saorbust

    saorbust Hardcore MB Enthusiast

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    Also check your oil levels. Takes so long to warm up the oil can burn off easily when the engine is very cold (particularly in diesels). I've just added a litre to mine - MPG has ticked up a little. Worth checking....
     
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  15. d w124

    d w124 MB Club Veteran

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    Did you check the car from the last time we`ve met?
     
  16. OP
    OP
    SHAKTER

    SHAKTER Hardcore MB Enthusiast

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    Hey Dash yes I noticed this only the other day. Was in a rush so only filled up £20 worth fuel. Basically 3.66 gallons (16.68litres). And I only got to 59 miles when the fuel guage light came on. So by my calcs thats only 16mpg!!

    Oil levels look fine. I'll get the car serviced when the weather clears up and see if that helps. I was just a little surprised that fuel economy is this poor to-date. Averaging 18mpg normally, 16mpg in the cold - when I bought the car I was expecting mid 20's at least!!
     
  17. tali

    tali Hardcore MB Enthusiast

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    But after fuel light you should be at v least get to 69miles -which equals 18mpg?
     
  18. BillyW124

    BillyW124 Hardcore MB Enthusiast

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    UPDATE:

    Filled up last week full tank again. I have now done 171 miles and my needle is exactly on half. That's 25 MPG so far MPG calculator UK miles per Gallon - calculate MPG

    I really dont know whats going on here. My MPG has improved dramatically as mentioned from my previous threads when i was going on about low MPG.

    A few factors to consider which I think or has improved it:

    • Throttle body clean
    • Use of Redex every full tank (this is debatable)
    • change of oil from previous service, used Mobil 1. Now using Castrol Magnatec.
    • kept in E mode as opposed to S on transmission
    • different use of petrol station...I use Texaco now rather than the local cheaper alternatives. I really am beginning to think that paying a few pence more for a better quality fuel works out better? I think they burn better, plus the car sounds and feels alot smoother?
    • and the obvious one, easy on the gas. Probably the main contributing factor to better MPG. Judge braking distances well and pull off the accelarator way before you want to stop on junctions/lights. (dont know if its just my 124 but sometimes my speed remains static if i lift off the pedel, the speed will remain there until the road unlevels itself or if I brake. Usually when in 4th gear i think. It's like cruise control but its not because i dont have it)
    • have a light foot on drive off, let the gear box engage gears smoothly.
    • i usually get up to second gear and lift off a let the car coast. The revs are usually at 10.5 when i lift. (you will see the rev needle drop and stay here) I find my self doing a good speed already at this point. If i have to accelerate more i just tap slightly to catch up with traffic etc.
    I have changed my driving habits for two tanks now and seems to do justice so far i think.

    Perhaps somebody can come along and probably explain how cheap fuel would differ from good quality fuels.

    Shell have devised a new unleaded which gets you a litre more from a tank..
     
  19. d w124

    d w124 MB Club Veteran

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    I always found better mpg by using super,so is well worth it
     
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  20. gIzzE

    gIzzE MB Club Veteran

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    That doesn't mean you have done 25mpg at all.

    You need to refill the tank and see how many gallons you have used to work it out, properly.

    An mpg gauge is not linear in its movement.

    I can do around 350 miles in my car by the time it gets to half way, however, I don't then get another 350 miles using the second half, usually 200 miles for that.
     

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