Turning Off at Lights & MPG

Discussion in 'General Discussion' started by flat6buster, Jul 11, 2011.

  1. flat6buster

    flat6buster Hardcore MB Enthusiast

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    Just out of interest I seem to recall ages ago being told that turning off a car and then restarting it used more fuel than just leaving it running (ignoring if we may the manufacturer start/stop systems).

    Is this true or poppycock? If there's some truth to it then I wonder what the time delay would be before it was worth turning the car off then restarting?

    I have 1 set of traffic lights on the way into work where my average mpg for the entire journey drops by a whole 1 mpg if I catch the lights wrong (it's a long long delay)

    Anyone here as dull as me but more intelligent and would know the answer?
     
  2. finisterre

    finisterre Hardcore MB Enthusiast

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    I would guess that your mpg parked and ticking over is pretty poor.
     
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  3. st4

    st4 Banned

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    If stopped for over 2mins its best to turn the engine off to save fuel, any less time, false exercise.
     
  4. OP
    OP
    flat6buster

    flat6buster Hardcore MB Enthusiast

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    Thanks that kinda what I thought but did not know for sure.

    It's an 18 mile commute and to have 1 set of lights knock a whole 1 mpg off seems horrendous to me.

    I thought diesels were meant to be economical but I guess if it has turbos and is 4 litres plus economy is always going to be a distant hope...!
     
  5. gIzzE

    gIzzE MB Club Veteran

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    What, you mean being 0mpg? :D
     
  6. renault12ts

    renault12ts MB Club Veteran

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    Has anyone really tested this?

    I mean engine off for a couple of minutes is not going to make a difference in the scheme of things, except for cleaner air. I wonder how much you would use if the car was left to idle for an hour. No load, no turbos etc...a litre or less ?

    Who has the time to try it?
     
  7. gIzzE

    gIzzE MB Club Veteran

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    I have bought a BMW X1 and that has stop start, exactly the same as turning the engine off on any other car, one thing though is it doesn't kick in until the engine is up to temperature, once up to temperature it is far more economical to turn off even if it is for 30 seconds.

    Problem you have with diesels is how long they take to get to temperature, a big 4 litre is going to take a good 15 minutes or 10 miles to get there even during warm weather, in the winter I bet you are only just getting up to temp by the time you get to work!

    I bet you are only getting about 26mpg at the moment and high teens to low 20s during the winter??
    I know a friend of mine who went from an ML500 to the GL420cdi and he only gained around 3mpg during the summer and was pretty much the same at winter.
     
  8. gIzzE

    gIzzE MB Club Veteran

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    On the X1 with stop start, and doing quite a bit of town work, I get around 530 miles with it off and just under 600 miles with it on. I didn't like it at first hence trying it off as I thought there could only be 1 or 2 mpg in it.
    However with it on I am sitting at 47mpg and off it is just under 41mpg.

    You would be amazed at the amount of time you sit doing 0mpg. On the way into the city it takes around 20 minutes and 5 mins of that is doing 0mpg at least. That seriously effects your overall consumption.
     
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  9. verytalldave

    verytalldave Hardcore MB Enthusiast

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    In the great scheme of things, turning engines off and on is going to makes gnats difference to cleaner air argument.

    I read somewhere that the volcanic eruption in Iceland a while back caused more airborne pollution and CO2 than ALL man's efforts since time began.

    Cars are such a minuscule part of the pollution debate.

    Volcanoes pose a MUCH bigger problem.
     
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  10. gIzzE

    gIzzE MB Club Veteran

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    They could fit them with DPF's, they must reach the temperatures needed to burn off the excess build up? :D
     
  11. snoop51

    snoop51 Hardcore MB Enthusiast

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    So what are you suggesting? Loads of cement tipped in the top of each one?:D:D
     
  12. renault12ts

    renault12ts MB Club Veteran

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    Simples... just ban volcanoes.
     
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  13. W4SIM

    W4SIM Banned

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    I heard once years and years ago (before Stop/Start was even thought of) that starting a car is the equivalent of 90 seconds of idling it. So 90 seconds to 2 mins seems about right, but thats probably more for the older cars.
     
  14. renault12ts

    renault12ts MB Club Veteran

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    It could work...but concrete is one of the least environmentally friendly substances known to man.
     
  15. clk208

    clk208 Hardcore MB Enthusiast

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    I suppose this is partly true. However, cars are much more of a problem for localised pollution and impact people directly. You only have to drive down the M1 or M11 towards central London in summer to see the bowl of smog that forms. Air quality can be so poor in central London folks find it noticeably harder to breathe. Seem to remember reading a report that black cabs are responsible for about a third of this, and having cycled behind many it seems feasible.

    Coming back to the original question, a friend of mine with an interesting job was assigned to basically spy on a location for a few hours on a hot day in summer and was stationed in a parked vw golf(diesel). He sat there with the car idling and a/c on for 3 hours and reckoned it had used well under 2 gallons of juice. I understand petrol cars sip a lot more fuel at idle.
     
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  16. W4SIM

    W4SIM Banned

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    I have a 2000 X reg Vectra thats a 2.0 DTi (sorry, but i just cant afford the S55k dream yet). Anyways, on the computer it shows the exact MPG your doing as your driving, so thats always flickering around, but if you stop and just idle it usually shows it as "0.2 Gallons per Hour". Which i think is about 1 liter, or maybe just slightly under. After a good motorway run for an hour or so iv seen that drop to "0.1 Gallons per Hour", which is about a half a liter.

    Thats an 11 year old 2 liter Turbo Diesel, newer engines should be better, bigger engines might come off slightly worse.
     
  17. verytalldave

    verytalldave Hardcore MB Enthusiast

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    When I worked at Rainham in Essex, driving home to Orpington (Kent) would take nominally about 45 minutes for 27 miles and during that time would average about 40 mpg.
    On the night that we had the really bad snow, my journey time was 8 hours and I averaged 8.5 mpg.
    Quite a difference.
     
  18. snoop51

    snoop51 Hardcore MB Enthusiast

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    I know and yet we pour it everywhere. Most of London wouldn't exist without it.:) Which wouldn't be a bad thing IMHO:devil:
     
  19. Benzmanc

    Benzmanc Hardcore MB Enthusiast

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    Well we are currently in nimes sof car has third of tank and have only spent 160 euros On fuel since leaving Manchester. Well impressed :bannana:
     
  20. artyman

    artyman Hardcore MB Enthusiast

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    Since an auto gearbox drags when in D, as indicated by the fact that the brake is required to prevent movement, there must be an implication for fuel consumption rather than putting it in N or P. Any views?
     

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