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Filling up ... full tank vs half tank

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  • nicolax
    nicolax Posts: 298 Forumite
    im seeing more and more queues for petrol here, was massive at sainsburys last week
    at the moment im using about £80 a month in petrol, although thats slowly going up! (a tank is about £40ish and lasts round 2 weeks)
    have no idea where i am driving though to use all that up though! but im getting an average mpg (around 40mpg per tank) so its not that the cars guzzling petrol!
  • marlot
    marlot Posts: 4,967 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    KierNet wrote: »
    Never heard of that before! Surely its going to be tiny amounts? Unless one person fell off and they wanted a reason for it?
    Was a major issue on the roundabout near the filling station here the day after the VAT rise - lots of people filling their diesel tanks to the brim then sloshing it out as they drove away.
  • reeac
    reeac Posts: 1,430 Forumite
    Ninth Anniversary Combo Breaker
    JQ. wrote: »
    Are there any mathmeticians out there that can actually work out the actual cost saving of a petrol car with 35mpg, weighing 1,250Kg, and a tank capacity of 55 litres?

    I don't think that maths alone would suffice. Additional weight will affect rolling resistance and power consumed during acceleration but wind resistance will remain unchanged. I suspect that manufacturers [car and tyre] have data on rolling resistance - perhaps including the effect of varying load but power consumed during acceleration opens up a plethora of scenarios. Simplest approach would be to do a certain journey with driver only and then repeat with driver plus 3 passengers aboard and see if you can detect a difference. If you can then repeat with 2 passengers etc. You'd need a quiet road so that varying traffic didn't interfere with the measurements. Not easy.
  • LandyAndy
    LandyAndy Posts: 26,377 Forumite
    Part of the Furniture 10,000 Posts
    Remember the difference in average weight carried between filling the tank and running it to empty compared with half filling it and running it to empty is only a quarter of a tank which is about 15 litres in a typical car, that is about 12kg I think.
  • jeferey
    jeferey Posts: 4,300 Forumite
    Mortgage-free Glee!
    Also I would have thought that if you only 1/2 fill the tank and fill up again when it's at about 1/4 (I try not go below a quarter full too often!) you end up with 3 trips to the petrol station for 3/4 of a tank) for every one who fills up to the top and runs down to 1/4.
    I fill to brim every time - can't be @rsed spending my time at petrol station - I fill up about once a month.
    If at first you don't succeed, try, try, try - oh bu99er that just cheat :D
  • Strider590
    Strider590 Posts: 11,874 Forumite
    edited 29 March 2011 at 3:49PM
    How about this genious solution......

    Fill the tank, pay as quickly as possible and then drive to a supermarket to do your weekly shop. ;)

    As opposed to:

    Put £3 worth of fuel in, leave car at pump, spend an hour in the shop section, come out with piles of over priced doughnuts and Gingsters pasties. :mad:
    (which will also make you fat and cost your more in fuel because your fat!)
    “I may not agree with you, but I will defend to the death your right to make an a** of yourself.”

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  • Ebe_Scrooge
    Ebe_Scrooge Posts: 7,320 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    The point that has been made many times above is perfectly valid - yes it'll make a difference, but a miniscule difference. As someone else said, you'll do far better by making sure your tyres are in good condition and correctly inflated.

    What CAN make a small but significant difference to fuel consumption is anything electrical. You don't get owt for nowt, basically if something is drawing a current, that current is produced by burning fuel. If the fuel is being used to generate electricity, it's not being used to provide forward motion. OK, that's an over simplification, but the principle is valid.

    So don't drive along with all your lights on and the rear windscreen demister switched on if you don't need them. Lights and demisters draw a fair amount of current, so will make a difference to fuel consumption. Air Con is another power-hungry beast - although this is less clear-cut, as driving with a window open creates a lot of drag, so probably wastes even more fuel than the air-con uses. Also you need to use air-con for about 10 minutes a week at least, to keep everything lubricated.

    Things like a radio or the heater fan obviously use current, but here you're back into the realms of it being so small that it's not really worth worrying about.

    Other than that, keeping your car well-maintained, driving sympathetically and not carrying unnecessary weight or roofracks will make far more difference than the weight of a few litres of fuel.
  • wolvoman
    wolvoman Posts: 1,179 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    nicolax wrote: »
    i, however, fill mine to the top (as long i have the money to!) as my arguement was that although it may cost slightly more to carry the extra weight, the petrol price will also go up by the time i next fill up, so im buying more at the lower price

    Good thinking.
    If your friend and yourself both drive the same car for the same mileage:

    Your friend:
    First fill (1/2 tank - 30ltrs) @ 130p a litre
    2nd fill (10 days later) @ 140p a litre
    3rd fill (10 days later) @ 150p a litre
    4th fill (10 days later) @ 160p a litre
    Total spend 120 litres - £174

    You:
    First fill (full tank - 60ltrs) @ 130p a litre
    2nd fill (20 days later) @ 150p a litre
    Total spend 120 litres - £168

    Of course only applies on rising prices (but they aren't exactly falling right now).
  • LandyAndy
    LandyAndy Posts: 26,377 Forumite
    Part of the Furniture 10,000 Posts
    The point that has been made many times above is perfectly valid - yes it'll make a difference, but a miniscule difference. As someone else said, you'll do far better by making sure your tyres are in good condition and correctly inflated.

    So don't drive along with all your lights on and the rear windscreen demister switched on if you don't need them. Lights and demisters draw a fair amount of current, so will make a difference to fuel consumption. Air Con is another power-hungry beast - although this is less clear-cut, as driving with a window open creates a lot of drag, so probably wastes even more fuel than the air-con uses. Also you need to use air-con for about 10 minutes a week at least, to keep everything lubricated.

    Things like a radio or the heater fan obviously use current, but here you're back into the realms of it being so small that it's not really worth worrying about.

    Other than that, keeping your car well-maintained, driving sympathetically and not carrying unnecessary weight or roofracks will make far more difference than the weight of a few litres of fuel.

    The weight saving represents about 1% of the weight of a Ford Focus. If all of that is translated into improved economy then you might improve it by 0.5 mpg. If you have to drive even the tiniest fraction out of your way to ever (half) fill up that advantage will be lost.

    Generally thought that below 40 mph = open a window, over 40 mph = use the aircon.
  • Strider590
    Strider590 Posts: 11,874 Forumite
    wolvoman wrote: »
    Good thinking.
    If your friend and yourself both drive the same car for the same mileage:

    Your friend:
    First fill (1/2 tank - 30ltrs) @ 130p a litre
    2nd fill (10 days later) @ 140p a litre
    3rd fill (10 days later) @ 150p a litre
    4th fill (10 days later) @ 160p a litre
    Total spend 120 litres - £174

    You:
    First fill (full tank - 60ltrs) @ 130p a litre
    2nd fill (20 days later) @ 150p a litre
    Total spend 120 litres - £168

    Of course only applies on rising prices (but they aren't exactly falling right now).

    Don't forget to factor in the enormous drain of using your headlights in the snow/fog/night, reduces MPG by 75%!!!!!! :o
    “I may not agree with you, but I will defend to the death your right to make an a** of yourself.”

    <><><><><><><><><<><><><><><><><><><><><><> Don't forget to like and subscribe \/ \/ \/
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