Gasoline Evaporation at the pump: full of hot air?

I don't usually read those emails that I get from friends that say "read this and pass it along." Normally I just delete them. But I got one the other day that I do not believe. It concerned the cost of gasoline. Basically this long-winded email made the following points.

TIPS ON PUMPING GAS

1. Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. All service stations have their storage tanks buried below ground. As such, the colder the ground, the more dense the gasoline gets. 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.
   I live in Arizona where it gets to be 115 degrees. This can't be real.

2. When you're filling up, do not squeeze the trigger of the nozzle to a fast mode. If you look you will see that the trigger has 3 stages: low, middle, and high. You should be pumping on low speed, 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 for your money.
   Great. Now I can wait in line 3 times as long while people fill their tanks.

3. Fill up when your gas tank is HALF FULL (or HALF EMPTY depending on how you look at it). The reason for this is, the more gas you have in your tank, the less air occupying its empty space. Gasoline evaporates faster than you can imagine. 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.
   It has not been my experience that miles per gallon goes down as my tank empties.

4. If there is a gasoline truck pumping into the storage tanks when you stop to buy gas, DO NOT fill up - 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 one seems a little more plausible; however, if it were significant, stations would close their pumps when their storage tanks were being refilled.

See why I normally just delete these things. This can't be real, can it? The union of concerned scientists does not mention these things in their green tips for helping save the planet at the pump. As Labs scientists, we want the truth. And despite what Jack Nicholson's character said in A Few Good Men, we can handle the truth. So what's the truth? Let's hear from some chemists out there: TheLabs@autodesk.com.

Hoping to lay this urban legend to bed is alive in the lab. Other sites list this one as "undetermined."

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