I got this from bigdog56e on the AMC Eagle Nest
1. Fill up your car or truck in the morning when the temperature is
> still cool. Remember that all service stations have their storage tanks
> buried below ground; and the colder the ground, the denser the gasoline.
> When it gets warmer gasoline expands, so if you're filling up in the
> afternoon or in the evening, what should be a gallon is not exactly a
> gallon. In the petroleum business, the specific gravity and temperature
> of the fuel (gasoline, diesel, jet fuel, ethanol and other petroleum
> products) are significant. Eve ry truckload that we load is
> temperature-compensated so that the indicated gallonage is actually the
> amount pumped. A one-degree rise in temperature is a big deal for
> businesses, but service stations don't have temperature compensation at
> their pumps .
>
> 2. If a tanker truck is filling the station'* tank at the time you
> want to buy gas, do not fill up; most likely dirt and sludge in the tank
> is being stirred up when gas is being delivered, and you might be
> transferring that dirt from the bottom of their tank into your car'* tank
> .
>
> 3. Fill up when your gas tank is half-full (or half-empty), because
> the more gas you have in your tank the less air there is and gasoline
> evaporates rapidly, especially when it'* warm. (Gasoline storage tanks
> have an internal floating 'roof' membrane to act as a barrier between the
> gas and the atmosphere, thereby minimizing evaporation .)
>
> 4. If you look at the trigger you'll see that it has three delivery
> settings: slow, medium and high. When you're filling up do not squeeze
> the trigger of the nozzle to the high setting. You should be pumping at
> the slow setting, thereby minimizing vapors created while you are pumping.
> Hoses at the pump are corrugated; the corrugations act as a return path
> for vapor recovery â€" from gas that already has been metered. If you are
> pumping at the high setting, the agitated gasoline contains more vapor,
> which is being sucked back into th e underground tank â€" so you're
> getting less gas for your money .
>
> Hope this will help ease your 'pain at the pump'.

It won't help at all. Below-ground temps are very stable and are only seasonally variable. Not from hour to hour during the day.

number 2 will then and number 3 on older cars

#2 is absolute garbage. That fuel is clean, and it'* filtered. Besides, fuel pumps don't draw from the bottom of the tank.

#3 has no bearing on us, as our systems are sealed against vapor loss. It'* best to fill at 1/4 tank for us, to make sure the fuel pump is properly cooled by immersion in fuel.

Your post serves a purpose though. Not everything you get in email or read on the internet has any truth to it.

Yes, I used to pump gas for a living. I managed the station before I left.
Yes, I've had physics and a college degree.

Most of what you posted is pure nonsense.

what about number 4

If you collected the vapors yourself, and took them home after your fillup and condensed the vapor back into a liquid, you might see a 'fog' of condensed liquid on the sides of the container, amounting to less than half a cent of fuel at most.

I think I'll expand a little bit of this
#1) 1 gallon of gasoline at 100degF will shrink to 0.976 gallons (almost 2-1/2%) when cooled to 60degF, the supposed standard temperature for calibration. While I don't think the temperature of the gasoline in an underground tank changes very much on a day-to-day basis, there is the consideration of the tanker truck that has just dumped a warm load into the underground tank, and also the ambient temperatures that the gasoline is exposed to while in the above-ground portion of the pump itself.
Our friends north of the border (Canada) have temperature-compensated pumps, and I hear the big complaint is that since the average annual temperature in a lot of places is well below the 60degF standard, they are getting short-changed as compared to not having temperature correction.

#2) If the underground tank has not been maintained, there is also probably some significant water that has accumulated through condensation, settling to the bottom hopefully below the level of the pick-up tube. The unloading operation could also stir the water up in addition to the crud.

#3) Back in the early days when fuel pumps were first put into tanks, I was advised to keep at least a quarter-tankful to keep the fuel pump submerged so it would run cooler and last longer. I don't know if this is still valid advice, but I sure don't want to think about a hot fuel pump in a pool of gasoline!

Don't know where you live, but they sure do here.

Modern Gas pumps have technology in place to not allow moisture to enter the system, unless the cap is loose on the fillup area of the underground tank, water is not going to enter the system.

The underground tank is huge and temperature changes wil only occour season to season, not on a daily basis.

Furthermore there are also filters in the underground tank so you wont ever be able to pump "sludge or whatever" into your car.

My fuel pump had never been changed before this wekeend. it was 14 years old and there was no sign of debris in the tank whatsoever.

I don't know about you, but on my dad'* last truck, there was a ton of stuff at the bottom of the tank,