Date: Mon, 27 Mar 2000 12:17:50 -0800
Subject: Re: Money saving

On Mon, 27 Mar 2000 15:00:19 +0800, "Alfred" <> wrote: >Hi, > >There is a notion that one should fill the gas tank at night, rather than >during day time, as the gas station sells by volume, instead of by mass. > >The effect is subject to the expansitivity of the fuel, which I don't have >any relevant data. Do you have that? > >And what do you think about this 'money saving' habbit? > > >Alfred > Where I work, we have underground storage tanks that are electrically monitored for volume, leaks, water etc. Whenever these tanks are filled, the system does an automatic update to record the increased volume. Part of this update includes a temperature reading and temperature "correction". Example: 9000 gallons (US) of gasoline is put into the tank. For the purposes of this example, lets say that the gas that is already in the tank is 68 deg F, and the "new" gas is 85 degF. The computer automatically calculates a "temperature corrected" for the new gas, that *will* shrink in volume. How Much? From the readings I have seen, this is usually in the range of 10 to 25 gallons on an 8 - 9 thousand gallon "fill-up". You do the math for your gas tank. It should be remembered that the gas in your tank is always expanding and contracting due to temperature changes. The fuel in the underground tanks tend to be warmer than the night air, so if you fill up at night, you will be getting a *slightly* "expanded" gallon, but this will quickly shrink when it cools to the ambient temperature. Reverse is true for daytime fill-ups. Cooler gas will expand to the increased daytime temps. The whole thing averages out pretty nicely. The cooler air of the night is better for combustion, but during the heat of the day, you have a "bigger" gallon. -- "Our eyes and hands and feet will give us the same assistance in doing mischief as in doing good; but it would not therefore be better for the world, that all mankind were blind and lame. Arms are not to be laid aside by honest men, because carried by assassins and ruffians; they are to be used the rather for this very reason." -George Campbell (1719-1796)

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