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  • A simple Petrol question (I think)
  • handyman153
    Free Member

    Morning..

    Probably a really easy question, but i have been thinking about it this morning. So thought i would ask the STW massive!

    Yesterday morning when i got to work, i had pretty much exactly 1/4 of a tank of petrol left.
    So after 9 hours, i got back in the car to go home, and i had about 3/8 – 1/2 tank left.

    Is this because –
    A) My car is a bit rubbish and old, it doesn’t really know how much fuel i have got.
    B) Fuel is like water (ice), and as it gets cooler expands slightly, therefore using more room.
    C) Other???

    Josh..

    stgeorge
    Full Member

    A

    cheburashka
    Free Member

    A.

    And hills are involved.

    PJM1974
    Free Member

    A

    5lab
    Full Member

    a – could also be a sign that your alternator or battery are on the way out, and on your drive into work thismorning (related to the cold weather) the electrics were running at lower voltage than normal, and there wasn’t enough juice to push the needle up as far as it needed to go (assuming car is old enough to have a fully analog fuel gauge)

    bigyinn
    Free Member

    Fuel gauges can take time to settle down if you’re on a hill etc then this will skew the readings.
    My last car the last quarter lasted a hell of a lot less than the 2nd quarter. Which just goes to prove its all just a gide only.

    stgeorge
    Full Member

    could also be a sign that your alternator or battery are on the way out, and on your drive into work thismorning (related to the cold weather) the electrics were running at lower voltage than normal, and there wasn’t enough juice to push the needle up as far as it needed to go (assuming car is old enough to have a fully analog fuel gauge

    This can’t happen as there will be a voltage regulator in the fuel guage circuit. (Just try it with engine off and engine stopped but ignition on – no difference in reading although voltages from electrics will be changed from 14 to 12.5 approx))

    Its the angle of fuel level relative to tank that causes it, ie hills, g forces etc

    molgrips
    Free Member

    Fuel gauges are completely rubbish, even in modern cars.

    PS water shrinks as it gets colder, only when it starts to turn into ice does it get bigger. It’s one of the many very unusual qualities that make water one of the more bizarre substances known to science, despite us taking it completely for granted.

    Petrol doens’t ‘freeze’ like water does, it would go waxy I think, and it doesn’t do that at any temperature found on earth.

    v8ninety
    Full Member

    My car does similar, this is my theory; the fuel gauge is fairly heavily damped, to stop it going up n down constantly when accelerating, braking and cornering with half a tank of fuel sloshing around. If I fill up without taking the keys out of the ignition it takes 5-10 minutes for the gauge to catch up. On my journey to work, quite a lot of sloshing, and the position of the float seems to be such that it spends more time in the shallow end than the deep end, so to speak. Hence given settling time, it seems to gain fuel. I often get home with the red light on, only for it to be off again on the next journey for the first 10-20 miles.

    stgeorge
    Full Member

    Spot on V8

    jam-bo
    Full Member

    fuel gauges are rubbish.

    my old 205, I could drive from taunton to manchester on the top quarter of the tank, and then barely make it back to birmingham on the rest.

    didnt have a working fuel gauge in my old golf for about the last 100,000 miles of its life, just worked off the trip and knowledge it did ~250 to a tank.

    bikebouy
    Free Member

    Theres Science in there somewhere:

    “Lunar Eclipse Effects on Earth and Petrol
    Lunar phase refers to appearance of an illuminated segment of Moon as seen via an observer, generally on Earth. In accordance with changing virtual positions of Sun, Moon and Earth, the lunar phrases differ cyclically as Moon orbits the Earth.
    The idea behind lunar effect has captivated many deeds lists and also warranted several studies and experiments. However, most experiments have set up no connection between variables and hence, disproved the theory.
    Conversely, the majority of methodical research seems to disprove the premise of lunar effect. The Psychologist Ivan Kelly of the University of Saskatchewan (with Roger Culver and James Rotten) did the meta- analysis of 37 studies that inspected associations between Petrol and the moon’s four phases. The meta-analysis exposed no connection.
    Astronomer Daniel Caton examined 70,000,000 Petrol litre records from National Center for Petrol Statistics, and no connection between moon phase and Petrol was found. Culver, Rotton, and Kelly report that Caton observed 45,000,000 Diesel litres and set up the weak peak just about the 3rd quarter phase of the Moon, whereas the new moon phases and full moon had a regular or vaguely below average litre rate.
    The word “menstruation” is etymologically connected with “moon”. And the terms “menses” and “menstruation” are derivative from Latin menses (month), which in order relates to Greek mane (moon) and to roots of English words month and moon—reflecting the verity that the moon takes near to 28 days to rotate around the Earth (actually 27.32 days). And The synodical lunar month, the time between two new moons (or full moons), is 29.53 days lengthy. Some authors suppose Petrol in cars in customary societies devoid of night light expanded with full moon and shrank with new moon. And a small number of studies in both cars and lorries have originated that artificial beam at night does persuade the bicycle and tricycle irider to spout bollox on occasion. Cyclists are extra regular in the deficiency of sensible thoughts at night), although none have established the harmonization of cycles with the lunar cycle. And one writer has suggested that compassion of cyclists to night light is caused through nutritional deficits of certain minerals and vitamins. The chemical imbalance of other animals may be significantly diverse from the lunar cycles: though the average cyclists duration in spouting bollox is the similar as it’s always been—28 days—the common for normal folk is 365 days. And a few take this as a confirmation that the regular length of humans’ cycle is almost certainly a coincidence.”

    B.A.Nana
    Free Member

    A. Mine’s the same, seems to have a spot for about 50 miles somewhere around the 1/4 mark where it can’t decided whether it’s nearly empty (needle doesn’t move at all, warning light on) or 1/4, so it kind of fluctuates between the two for a while, to hedge it’s bets.

    epicyclo
    Full Member

    Magic fuel tank.

    Someone from the oil cartels will be around shortly. Expect to receive a large financial offer or assassination.

    😆

    dan1980
    Free Member

    Petrol doens’t ‘freeze’ like water does, it would go waxy I think, and it doesn’t do that at any temperature found on earth.

    The only substance that won’t freeze in standard atmospheric conditions is helium.

    For something to freeze, it undergoes a phase transition from liquid to solid. A wax is a solid.

    Petrol will freeze around 210 Kelvin (Approx -60 Celcius)

    Interestingly (for me anyway), the fuel gauge on my motorbike seems to operate with a fairly long delay, and if I brake hard I can “gain” half a tank of petrol for about 30 seconds :mrgreen:

    5lab
    Full Member

    This can’t happen as there will be a voltage regulator in the fuel guage circuit. (Just try it with engine off and engine stopped but ignition on – no difference in reading although voltages from electrics will be changed from 14 to 12.5 approx))

    whilst that would stop any voltage over, say, 12v getting to the gauge, would it help if there were less than 12v available to start with?

    molgrips
    Free Member

    The only substance that won’t freeze in standard atmospheric conditions is helium.

    Er, standard atmospheric pressures perhaps, but lots of things don’t freeze at temperatures found on earth ie above about -90C

    For something to freeze, it undergoes a phase transition from liquid to solid. A wax is a solid.

    Oh it is, is it? 🙂

    Btw the waxing point of petrol depends a lot on what’s in it. It’s a mixture of lots of different things all wiht differen tproperties.

    stgeorge
    Full Member

    whilst that would stop any voltage over, say, 12v getting to the gauge, would it help if there were less than 12v available to start with?

    I think they regulate it down to 5-7 volts, to avoid guage fluctuations due to voltage fluctuations.

    If it goes lower than this you aint going anywhere anyway 😀

    v8ninety
    Full Member

    A wax is a solid

    Actually a supercooled liquid? ( 8) ) like glass n stuff?

    Don’t know, just asking…

    IHN
    Full Member

    According to my fuel gauge, the top quarter of my tank is the same size as the bottom three-quarters…

    hels
    Free Member

    Electrics.

    Random fuel guage was the first sign of electrics trouble in one of my cars.

    molgrips
    Free Member

    Supercooled liquid, yes. That’s why as it cools it just gets thicker and thicker, rather than crystallising suddenly like water does.

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