With GAS expected to reach $5 per gallon by summer, these tips that I received from a friend might come in handy.
TIPS ON PUMPING GAS
#1 Only buy gas or fill up your car/truck in the EARLY MORNING when the ground temp. 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 temp. of the gasoline, diesel and jet fuel, ethanol and other petroleum products play 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.
#2 Don't squeeze the trigger of the nozzle to a fast mode. If you look you will see that the trigger has three (3) stages: low, middle, and high. You should be pumping on the low mode, thereby minimizing the vapors that are created while you are pumping. All hoses at the pump have a vapor return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapor. Those vapors are being sucked up and back into the underground storage tank so you're getting less worth for your money.
#3 Fill up when your gas tank is HALF FULL. The reason for this is the more gas you have in your tank the less air occupying its empty space. Gasoline storage tanks have an internal floating roof. This roof serves as zero clearance between the gas and the atmosphere, so it minimizes the evaporation.
#4 DO NOT FILL UP if there is a gasoline truck pumping into the storage tanks when you stop to buy gas. Most likely the gasoline is being stirred up as the gas is being delivered, and you might pick up some of the dirt that normally settles on the bottom.
This info. comes from a friend who works at the Kinder Morgan Pipeline in San Jose, CA where about 4 million gallons are delivered in a 24-hour period thru the pipeline. They have 34-storage tanks with a total capacity of 16,800,000 gallons.