ORIGINAL: Cuda340
Only buy or fill up your car in the early morning when the
ground temperature is still cold. Remember that all service stations
have their storage tanks buried below ground. The colder the ground the
more dense the gasoline, when it gets warmer gasoline expands, so buying
in the afternoon or in the evening....your gallon is not exactly a
gallon. In the petroleum business, the specific gravity and the
temperature of the gasoline, diesel and jet fuel, ethanol and other
petroleum products plays an important role. A 1-degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps.
Realistically, this is more theoretical than actual. Even at 6 to 7 feet below ground, the temperature is pretty constant. Hence, one day's external temperatures don't have a lot of impact on the temperature of the gasoline underground. (I remember working in gas stations in Iowa during the winter and it took weeks of winter weather before the gasoline started feeling any colder -- and even then it wasn't REAL cold.) About the only thing that can be affected by one day's changing temperatures is the pump itself and the hose going into your car. And say on a warm day at a high-volume station, the regular flow of gas from underground through a pump and its hose keeps the insides of the unit pretty well cooled off, so there actually isn't a lot of temperature change internally.