How do u guys calculate miles per gallon?

[diamondlarry]

Originally Posted by fuelmiser

i appreciate everyone's reply to this thread. thank you! it gives me an idea of everyone's thought process. i didnt know the fuel tank area was so complex. but from what im gathering..i conclude that consistency is the most important variable when filling up.

one thing noone mentioned is...after filling up the tank...go to each four corners of the car and give each corner a couple of bounces to get rid of "Air Pockets"...is this myth true? things that make u go hmmm...

I wouldn't say that you have to go to all 4 corners but I do shake my car by grabbing the fenderwell and quickly shaking it up and down. I keep doing this until the level in the filler doesn't change for at least 10 seconds after the shaking. I just like to be consistent.

HEK, interesting thought on the ramp thing.

[rearviewmirror]

https://www.fueleconomy.gov/mpg/MPG.do

[Bill in Houston]

You could easily make a little ramp 4 inches tall from two pieces of 2x4, and just lift the corner or the car where the fill port is. Not worth the hassle to me, though.

[Bennet Pullen]

rGS, wouldn't the temperature related expansion/contraction properties have just as much a factor on accuracy using the first click method as the top off method? Overflow concerns aside the gas will still expand and contract the same no matter which way you fill your tank.

Responding to diamondlarry, one of the local news stations in my area did a piece on gas pump accuracy last summer when gas prices spiked. They found that the slower you pump the gas, the more accurate the gauge was. Keep in mind they were filling up graduated cylinders with gas and weren't even using the automatic cutoff. So I guess I would say yes speed makes a change, I personally always use the first (slowest) hold position on the nozzle.

I also fill up using the "second click" method, where you fill to the first click, wait a bit for bubbles, waves, etc to clear and fill slowly to the click again. I think this method will be more accurate (especially between pumps) than the first click because it takes out some of the variables of frothing etc.

[diamondlarry]

Originally Posted by Bennet Pullen

rGS, wouldn't the temperature related expansion/contraction properties have just as much a factor on accuracy using the first click method as the top off method? Overflow concerns aside the gas will still expand and contract the same no matter which way you fill your tank.

Responding to diamondlarry, one of the local news stations in my area did a piece on gas pump accuracy last summer when gas prices spiked. They found that the slower you pump the gas, the more accurate the gauge was. Keep in mind they were filling up graduated cylinders with gas and weren't even using the automatic cutoff. So I guess I would say yes speed makes a change, I personally always use the first (slowest) hold position on the nozzle.

I also fill up using the "second click" method, where you fill to the first click, wait a bit for bubbles, waves, etc to clear and fill slowly to the click again. I think this method will be more accurate (especially between pumps) than the first click because it takes out some of the variables of frothing etc.

I think that I agree that this would be somewhat more accurate/consistent than the 1st-click method. Foaming/turbulence would be much less of a factor using this method. I usually don't even go all the way to the first notch when I'm pumping my gas unless I'm in a hurry which rarely is the case.

[GasSavers_rGS]

Originally Posted by Bennet Pullen

rGS, wouldn't the temperature related expansion/contraction properties have just as much a factor on accuracy using the first click method as the top off method? Overflow concerns aside the gas will still expand and contract the same no matter which way you fill your tank.

Bennet Pullen,

It's a matter of the laws of physics limit called "maximum volume" in other words 100%. So let's say you fill up the tank to 100%. Then the gas expands. Since the tank can't physically expand proportionally as fast as the gasoline so the gas can remain in the tank and therefore no wasted gas, the reality of the situation is that the gasoline WILL overflow. That's because the material property of gasoline expands and also contracts at a faster rate than the expansion and contraction rate of the metal used to make the gas tank. That overflowed gas will literally be a WASTE which is effectively the same thing as driving non-fuel efficiently which we're trying to avoid. So, once the fuel is wasted it's wasted and that means wasted money on gas that you didn't use.

However, by using the first click method, you fill your gas tank up to the "full point" that was calculated by the engineers so that even with gas expansion due to hot temperature, the gasoline shouldn't expand more than the capacity of your gas tank. What that means is that more of your gas remains in your gas tank and therefore is NOT wasted. Therefore since the gas is NOT wasted your money you paid for the gas isn't wasted either.

[Bill in Houston]

This thread totally went down the rabbit hole, huh?

[zpiloto]

Originally Posted by Bill in Houston

This thread totally went down the rabbit hole, huh?

No kidding. Do we take the red pill or the blue?

[brucepick]

Yes it went down the rabbit hole.

Anyway, I'm with rGS.
I like a nice simple fill to the first click. I fill kinda slow to avoid lots of chaos going on inside the tank. Also to avoid splash that will be pulled back out via the vapor recovery system (just a theory of mine).

I think this is probably more consistent than using two clicks or till you see gas at the top of the fill tube. Not much is worse than spilling the fuel. Duh! Any inaccuracies should even out pretty easily.

[96hb]

Are these few tenths variations really going to make that big a difference? I don't think so. Whatever way you choose to fill up, just do it consistently and you will be fine.