As a general rule, if you want to save money, fill your car tank at night when it is cold rather than at noon when it is hot. The price of gasoline is fixed per unit of volume (gallon-liter) and not per unit of solid mass (Kg).

Assuming a high temperature difference between day and night of 20 ° C and a volumetric thermal expansion coefficient of 0.00095 for gasoline and 0.00125 for good quality benzene, a gallon at night increases up to 1.025 gallon at noon, which represents a saving of about 2.5% on fuel prices ($ 2.55 / gallon in the United States or $ 5.6 / gallon in Europe).

Is this saving worth it? If yes, how much will your bill be reduced in a month or a year?

  • 4
    You seem to be assuming that the temperature of the gas would match the temperate of the air. That probably wouldn't be the case since the gas is usually stored in under-ground tanks. I would suspect that the temperature would be the same (negligible difference) no matter the time of day.
    – Nosjack
    Dec 19, 2019 at 21:42
  • 2
    This is not a website where you can just copy+paste your homework problems. Try to solve it yourself first, and if you stuck, ask about the part where you are stuck (showing all the work you've done so far).
    – Ben Voigt
    Dec 19, 2019 at 21:50
  • Nosjack- The gas is mostly stored in underground tanks but the temperature varies substantially day and night specially in desertic areas I suppose. Thanks for the comment .
    – Lionheart
    Dec 19, 2019 at 21:52
  • Nosjack-This is subtle question since the temperature difference of the fuel tank itself differs from place to place and tank to tank.
    – Lionheart
    Dec 19, 2019 at 21:58
  • .Temp.difference of the fuel itself is not an easy task to calculate.
    – Lionheart
    Dec 19, 2019 at 22:05

1 Answer 1


The answer is 'about zero'.

Most gas stations have a sticker that claims that 'the sale volume is corrected for temperature', so unless that is a lie or it is malfunctioning, you won't have any advantage. Although probably the waiting lines are shorter at 4 am.

  • Aganju-This is the correct answer we are looking for.Only if you can find a station without temp correction you get the advantage. Thanks for your clever answer.
    – Lionheart
    Dec 19, 2019 at 22:26

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