ripped off at the pump?

**DrMilhouse** · 07-25-2008, 10:06 AM

Anyone else ever have a concern that a "gallon" at the pump might not be the standard 1 gallon?

I'm just wondering, but since I started using e-85, I'm going to a new place and I'm filling up. I've had my car pretty low before, but no matter how low it's been, I've never had to put 15.5 gallons of gas in my car even though the needle has been in the same place before.

With the mileage arguement set aside and the whole e-85 arguement set aside really, does anyone else ever wonder if we're getting screwed at the pump by a different definition of a "Gallon"?

What do you do to prove it?

**Spaz** · 07-25-2008, 10:08 AM

Originally Posted by DrMilhouse

Anyone else ever have a concern that a "gallon" at the pump might not be the standard 1 gallon?

I'm just wondering, but since I started using e-85, I'm going to a new place and I'm filling up. I've had my car pretty low before, but no matter how low it's been, I've never had to put 15.5 gallons of gas in my car even though the needle has been in the same place before.

With the mileage arguement set aside and the whole e-85 arguement set aside really, does anyone else ever wonder if we're getting screwed at the pump by a different definition of a "Gallon"?

What do you do to prove it?

this happens all the time... on the east coast here NJ to be exact there were SEVERAL stores that were charged for doing this...

**gwballin** · 07-25-2008, 10:10 AM

Originally Posted by DrMilhouse

Anyone else ever have a concern that a "gallon" at the pump might not be the standard 1 gallon?

I'm just wondering, but since I started using e-85, I'm going to a new place and I'm filling up. I've had my car pretty low before, but no matter how low it's been, I've never had to put 15.5 gallons of gas in my car even though the needle has been in the same place before.

With the mileage arguement set aside and the whole e-85 arguement set aside really, does anyone else ever wonder if we're getting screwed at the pump by a different definition of a "Gallon"?

What do you do to prove it?

Well, there are 16 cups in a gallon. I say you get a measuring cup out of the kitchen go to the station and test it. Lets us know what you find.

**B34M3R** · 07-25-2008, 10:13 AM

Most places calibrate the pumps to the coldest time of the day... as the temp goes up the actual amount of gasoline you get decreases... there was a HUGE fuss about that in FL this year....

Fill up at night or in the morning if possible... if you fill up in the afternoon you wont get as much gas.

**Mr. Luos** · 07-25-2008, 10:25 AM

Originally Posted by Spaz

this happens all the time... on the east coast here NJ to be exact there were SEVERAL stores that were charged for doing this...

Here too.

I remember reading about it on 9news.com. The state apparently fined several local stores a few months ago...and apparently has random people going around and testing fueling stations.

Originally Posted by B34M3R

Most places calibrate the pumps to the coldest time of the day... as the temp goes up the actual amount of gasoline you get decreases... there was a HUGE fuss about that in FL this year....

Fill up at night or in the morning if possible... if you fill up in the afternoon you wont get as much gas.

I thought I read that was bogus. Just a rumor.

**SpecterGT260** · 07-25-2008, 10:25 AM

liquid thermal expansion is really pretty small. while this is all technically true i dont think you are going to be able to notice it if its due to just the temps.

if you are really getting an appreciable difference in what ur getting and what the pump reads u could take this up. even a discrepency of 1 cup is enough to claim a miscalibration

**B34M3R** · 07-25-2008, 10:30 AM

Liquid thermal expansion is small... but the fact when the main tanks are running low alot of the liquid gas turns into vapors, then the expansion effects you more.

I dont remember the exact numbers, but the state looked into it bitch slapped a bunch of stations because it was a serious problem.

**Spaz** · 07-25-2008, 10:38 AM

Originally Posted by Mr. Luos

Here too.

I remember reading about it on 9news.com. The state apparently fined several local stores a few months ago...and apparently has random people going around and testing fueling stations.

as soon as one gets fined the rest say "we are ok to do this now cause some one else took the heat for it" and they are probably right... they aren't going to do another check/test in a while...

**Mr. Luos** · 07-25-2008, 10:47 AM

No idea how true it is...but the news report said they nailed the same station like 3 times in 6 months, so they were going back to the same place.

From what they said, the State of Colorado employs several people to 'secret shop' the stations.

**SpecterGT260** · 07-25-2008, 10:47 AM

the thermal expansion of gasonline is .069% (thats .00069) per degree F (from what i just read) so lets say they calibrate @ 55 degrees and you fill up at 90 degrees at high noon. thats 35 degrees.

1 cubic meter of gasoline will change volume by (1 m^3)(1+ .00069*35 degreed)

thats 1.02 so that meter expanded by .02 m3. thats 2% expansion in 35 degrees which is a pretty damn big gap.

so to put it into US units, you get 10 gallons of gasoline calibrated like this, you really only got 9.8

actually..... .2 gallons is 3.2 cups so that is kinda measurable. but thats calibrated with a 35 degree difference. I dont know what the standard procedures are. one article said they use a 60 degree standard so if u are in the 70s or so you wont feel it too much.

**DrMilhouse** · 07-25-2008, 11:00 AM

that's a 35 degree difference in ambient outside temprature. The thermal expansion of the gas would have a bit more to do with the actual temprature of the gas at the gas, not the temp of the outside. Of course I could be wrong, I don't know much about that stuff.

**SpecterGT260** · 07-25-2008, 11:06 AM

the gas will be pretty damn close to whatever the underground tank's temp is which will probably be colder than ambient air in the summer. the pump itself shouldnt generate a ton of heat either. and all measurements are made within the pump so once it comes out the nozzle it can expand as much as it wants without affecting the calculations

in fact, if it expands AFTER being pumped it will appear that you got the right ammount

**SpecterGT260** · 07-25-2008, 11:08 AM

also, this shouldnt affect your actual volume. i guess we werent being clear on that. you will in fact get 10 gallons if you pump 10 gallons, but it will be less dense. same principle as getting a CAI. that was my bad.... i wasnt thinking straight on that one. there isnt going to be a way to measure it at the pump. in fact, i dont think the pump calibration has anything to do with it now that I think about it.

the article i read mentioned that gas is wholesaled per volume at a standard 60 degrees. and that is how the price is set. so lets go back to this 35 degree difference yeilding 2 percent change. if the oil company sells a barrel of gasoline contianing 55 gallons measured and priced at 60 degrees, and you later purchase gas from this barrel in 95 degree weather, you are losing 2 percent of your purchase.

to put it another way, they say this drum contains 100 gallons of gas at 60 deg and costs 100 dollars. they ship it to california and you buy 10 gallons in 95 degree weather. they then take this drum back to the factory for whatever reason and cool it back down to 60 degrees, the remaining volume will be 90.2 gallons, not 90 gallons, because you lost 2% of your purchase. this 2% remains with the gas company to be resold.

the issue is not in the volume you get in your tank, but that the COST of the gasoline is set on a more dense substance. so when it finally gets to you you are buying gas that is less dense and contains less energy

so in light of that, if there is ANY discrepency between what the pump says and what u get in a bucket the pump is miscalibrated.

the expansion thing may be a real issue, but it wont throw off the pump, it will just throw off the price

**DrMilhouse** · 07-25-2008, 11:09 AM

So I should buy a gallon of gas in a can, take it home immediately and measure to make sure there's 16 cups in it? Any other ideas?

**GULLETT17** · 07-25-2008, 11:17 AM

im bringin a gallon milk jug with me everytime i fill up. . .

**SpecterGT260** · 07-25-2008, 11:18 AM

that should work if u want to call out a gas company for having bad pumps. a liquid pump measures volumes, it doesnt measure weight and convert to volumes. so for each pump (i dont know the parts inside but im assuming it has a wheel style pump or something) each rotation of the pump is designed to move a specific volume independent of weight or density so if 1 turn of the pump moves 1 gallon it will tell the machine to read 10 gallons after 10 pumps. if they miscalibrate then maybe its telling the machine 1.1 gallon per turn, thats where they can get dinged