# How much money can you save by buying gasoline at a different time of day? [closed]

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?

• 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. Commented Dec 19, 2019 at 21:42
• 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). Commented 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 . Commented 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. Commented Dec 19, 2019 at 21:58
• .Temp.difference of the fuel itself is not an easy task to calculate. Commented Dec 19, 2019 at 22:05