Pass Gas Slowly
 

Is is really true that filling up slowly gives you more gasoline because doing it at the high rate makes foam, which means that there is more air mixed in with your gas?

No

No. Think about blowing bubbles in milk versus water. Bubbles in gasoline would go away too quickly to cause foam.

I have no idea, but thanks for the laugh with the clever title :)

Filling up at a higher rate causes the fuel to splash, which sometimes trips the sensor and shuts the pump off.

( Pull my finger )

No you will not get air mixed in your gas.
Like robbiewt said, it's more like blowing bubbles in watter, the bubbles will NOT last long.

but... as your filling the air that is in the tank needs to come out as the gas takes up the space. the air rushing out faster due to a fast fill can "Some times" in "Some cars" can cause some gas to get splashed back onto the fill nozzle. the pump will shut off thinking fuel is now up to the nozzle and shut off to prevent an over flow.

in the past I have had cars that if I did not place the nozzle in the fill tube at the right angle the air would catch some of the gas and shut off the pump to soon.
at some point you will have a pump shut off to soon and it's most always due to air rushing out.

to avoid that and get a fill to a consistent point each time I pump slow. less splashing = more consistent fill point = better ability to accurately calculate my FE.

Thanks! It's bean good learning :)

I've always pumped at the first auto-click in the handle, only to prevent loss of fuel from splashing and overflow.

The actual issue with pumping quickly (whether it's true or not, I suspect not) is not foaming, it's vaporization. The idea is that the faster you pump your gas, the more quickly it vaporizes, and the more of it you lose due to evaporation.

The idea is probably somewhat correct, but the time differential sets it off - If you take longer to pump, even though you're creating less vaporizing turbulence, you're giving the fuel more time to vent into open air.

If you pump faster, you're creating more fuel turbulence, which might vaporize more fuel, but you're giving the bulk of the fuel less air-time to vent.

It's probably a wash.

The other issue is that fuel pumps are certified with a margin of error, maybe +/- 1%... the pump is more likely to "break even" at a slower speed.

When you pump from a preset, most pumps now slow down when you get within about 1/2 gallon of that preset amount, so they don't cut off too soon or go over. Keeps you closer to being "on the dot".

Just avoid the problem entirely. My car has a 10-gallon tank. If I put the nozzle on its slowest setting, that gives me just enough time to wash the windows while it fills :-)

I always thought there was a vapor catch in the pump somewhere and it is designed to catch any vapor that may have come from the giant tank underground and recirculate it back into the tank, so that you don't get this bubble of air/vapor into your tank and have the pump count it as gas. I've noticed that I do get these bubbles out the nozzle when I pump at full speeds, so I put it on the lowest setting to allow it to trap all those vapors and get me more gas.

Plus, I get more time to get those bugs off the windshield! :thumbup:

I think there is a vapor filter in the tank, before the pump, but I can't verify that.