Common Glitch at Pump adds to Gas Costs

[RebelMan]

http://biz.yahoo.com/ap/080426/bad_gas_pumps.html

[MSFixR]

Another little known fact: gasoline is sold by volume yet the internal combustion engine extracts the energy in the gasoline on the basis of the number of moles of gas being combusted in the engine's cylinders. A mole of anything is 6.23E23 molecules and is directly related to the molecular weight (gasoline is a petroleum fraction and hence a mixture of compounds mainly hydrocarbons, therefore strictly speaking the number of moles in a specific volume cannot be calculated without an exact analysis of the ratio of the individual components in the gas). The volume of most liquids change inversely with temperature, i.e., the warmer the liquid, the larger volume a specific weight of the liquid will occupy. Therefore, the pump dispenses more gasoline when the gasoline is cool, i.e., early in the morning or late at night rather than during the day.

Several years ago I prepared a spreadsheet which takes into consideration the cost per gallon of the gasoline, the fuel efficiency of the automobile, the difference in driving distance between two competing gas stations, the amount of gas purchased and the difference in price per gallon between the two gas stations. If anyone is interested, PM me and I'll send it to you (somehow). The bottom line is that there is usually no advantage to driving around looking for the cheapest price.

[open32]

I do watch the meters most of the time. I was at gas station not too long ago when it registered my fill of around 13.2 gallons. I have a 13 gallon tank, and I know its never totaly empty.

[Jocasta]

Another little known fact: ... Therefore, the pump dispenses more gasoline when the gasoline is cool, i.e., early in the morning or late at night rather than during the day.

I did know that but when it take over $110 to fill my mid sized 2l diesel Audi you do care about these things.