# Gas Pumping Tips. Any truth?
**URL:** https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872
**Category:** Factual Questions
**Created:** [November 27, 2007, 2:54am UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872 "2007-11-27T02:54:17Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)
#### Post date: [November 27, 2007, 2:54am UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/1 "2007-11-27T02:54:17Z")
" Here at the Kinder Morgan Pipeline where I work in San Jose, CA we
deliver about 4 million gallons in a 24-hour period thru the pipeline.
One day is diesel the next day is jet fuel, and gasoline, regular and
premium grades.
We have 34-storage tanks here with a total capacity of 16,800,000
gallons.
Only buy or fill up your car or truck in the early morning when the
ground
temperature is still cold. Remember that all service stations have
their
storage tanks buried below ground. The colder the ground the more dense
the gasoline, 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. A 1-degree rise in temperature is a big deal
for this business. But the service stations do not have temperature
compensation at the pumps.
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 three (3) stages:
low,
middle, and high. In slow mode 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 worth for your money.
One of the most important tips is to fill up when your gas tank is HALF
FULL or HALF EMPTY. 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. Unlike service
stations, here where I work, every truck that we load is temperature
compensated so that every gallon isactually the exact amount.
Another reminder. 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."
---
### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [November 27, 2007, 3:02am UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/2 "2007-11-27T03:02:13Z")
It’s all bullshit, pretty much.
1. Underground tanks have VERY little in the way of daily temperature swings. In any case, gas dispensers are temperature-compensated. Periodic Weights and Measures checks ensure the accuracy of dispensers.
2. Vapor production is dependent upon temperature and vapor pressure. Pumping rate has negligible effect on how much vapor is produced.
3. The amount of vapor even a fully empty tank can hold under normal conditions of temperature and vapor pressure would reduce to a few cc’s at most.
4. Gas dispensers have fuel filters to keep tank sediment from getting into your car.
---
### Author:  [@mks57](https://boards.straightdope.com/u/mks57)
#### Post date: [November 27, 2007, 3:10am UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/3 "2007-11-27T03:10:37Z")
I can verify the bit about not buying gas while they are off-loading the gas truck. I ruined a carburetor when I ignored that advice and ended up with a ton of crud in the fuel system. That might have been the gas station’s fault for letting crud accumulate in their fuel tanks. How often do they clean the junk out of their fuel tanks?
---
### Author:  [@Rhubarb](https://boards.straightdope.com/u/Rhubarb)
#### Post date: [November 27, 2007, 3:26am UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/4 "2007-11-27T03:26:50Z")
[QUOTE=Q.E.D.]
It’s all bullshit, pretty much.
.
.
.
4) Gas dispensers have fuel filters to keep tank sediment from getting into your car.
[/QUOTE]
I agree they are _supposed_ to have such filters. They are even supposed to have baking soda filters that shut off the pump if there is water, instead of gasoline, in the system. Nevertheless, earlier this year I pumped 8 gallons of water mixed with sludge into my tank at $2.879 per gallon. I now mistrust gas station filters.
but on points 1 through 3, I totally agree.
---
### Author:  [@tonedef](https://boards.straightdope.com/u/tonedef)
#### Post date: [November 27, 2007, 1:00pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/5 "2007-11-27T13:00:16Z")
So if this was all true, I would be lucky to save a few $$ in my lifetime.
Worse thing that has happened to me when buying fuel and now I will only buy fuel from places are go threw alot of fuel so the tanks are beings refilled frequently. Because I got fuel in my tank that had gone off. I got horrible mileage an my care ran a bit rougher.
---
### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [November 27, 2007, 1:37pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/6 "2007-11-27T13:37:26Z")
**Q.E.D.** nailed it in one. The only thing I would add is that cars also have huge fuel filters now a days to keep crap out of the fuel injectors.
---
### Author:  [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)
#### Post date: [November 27, 2007, 1:59pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/7 "2007-11-27T13:59:35Z")
[QUOTE=Q.E.D.]
…gas dispensers are temperature-compensated. Periodic Weights and Measures checks ensure the accuracy of dispensers.
[/QUOTE]
What is the baseline temperature used to calibrate these? That is, at what temperature do you get a true gallon when the gauge indicates 1 gallon?
---
### Author:  [@pullin](https://boards.straightdope.com/u/pullin)
#### Post date: [November 27, 2007, 2:14pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/8 "2007-11-27T14:14:29Z")
I’m waiting for someone to explain the workings of an internal floating “roof” in an underground tank. Every (underground) tank I’ve seen is in the shape of a cylinder lying on its side. How exactly does this magic roof work?
I call BS.
pullin (who used to drive airport tanker trucks and filled them from underground storage tanks)
---
### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [November 27, 2007, 2:23pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/9 "2007-11-27T14:23:12Z")
[QUOTE=CookingWithGas]
What is the baseline temperature used to calibrate these? That is, at what temperature do you get a true gallon when the gauge indicates 1 gallon?
[/QUOTE]
In Canada it is 15C. I saw this posted on a pump yesterday.
---
### Author:  [@Balthisar](https://boards.straightdope.com/u/Balthisar)
#### Post date: [November 27, 2007, 2:32pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/10 "2007-11-27T14:32:14Z")
[QUOTE=pullin]
I’m waiting for someone to explain the workings of an internal floating “roof” in an underground tank. Every (underground) tank I’ve seen is in the shape of a cylinder lying on its side. How exactly does this magic roof work?
[/QUOTE]
I think he means a bladder that the distribution center, not at the gas station, right?
---
### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [November 27, 2007, 2:46pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/11 "2007-11-27T14:46:52Z")
[QUOTE=Rick]
In Canada it is 15C. I saw this posted on a pump yesterday.
[/QUOTE]
I _think_ it’s either 20 or 25 C here in the US. But, don’t quote me on that; I’m going from memory here.
---
### Author:  [@Hampshire](https://boards.straightdope.com/u/Hampshire)
#### Post date: [November 27, 2007, 3:07pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/12 "2007-11-27T15:07:28Z")
If filling an empty tank in “fast-mode” at any time of the day I want is going to cost me an extra 10 cents every time I fill up I seriously could not care less.
My personal convenience is worth 10 cents a week.
---
### Author:  [@Zsofia](https://boards.straightdope.com/u/Zsofia)
#### Post date: [November 27, 2007, 3:26pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/13 "2007-11-27T15:26:25Z")
[QUOTE=Rhubarb]
I agree they are _supposed_ to have such filters. They are even supposed to have baking soda filters that shut off the pump if there is water, instead of gasoline, in the system. Nevertheless, earlier this year I pumped 8 gallons of water mixed with sludge into my tank at $2.879 per gallon. I now mistrust gas station filters.
but on points 1 through 3, I totally agree.
[/QUOTE]
Yeah, me too. You know, the car doesn’t run if it isn’t _gas_ that you put in it?
---
### Author:  [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)
#### Post date: [November 27, 2007, 3:41pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/14 "2007-11-27T15:41:47Z")
Good points all around. The part that got me was that gasoline evaporates “faster than I can imagine.” I may not have the best imagination in the world, but I can use said imagination to envision an entire tank of gas evaporating in less than a second. I’m pretty sure it doesn’t really evaporate that fast.
Also, isn’t the fuel tank pretty air tight? If all the volatile portions of the gas evaporated away, your whole tank might be gone when you park at the mall for a couple hours in the summer!
---
### Author:  [@The\_Controvert](https://boards.straightdope.com/u/The_Controvert)
#### Post date: [November 27, 2007, 4:18pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/15 "2007-11-27T16:18:19Z")
[QUOTE=Mangosteen]
"
One of the most important tips is to fill up when your gas tank is HALF
FULL or HALF EMPTY. 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…"
[/QUOTE]
I would think the mileage cost of always hauling around a half tank of gasoline would offset the evaporation effect. Also, there is an inconvenience factor and gas cost to make additional side trips to the gas station.
---
### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [November 27, 2007, 5:24pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/16 "2007-11-27T17:24:53Z")
[QUOTE=Santo Rugger]
Also, isn’t the fuel tank pretty air tight? If all the volatile portions of the gas evaporated away, your whole tank might be gone when you park at the mall for a couple hours in the summer!
[/QUOTE]
Gasoline is volatile, to be sure, but it’s nowhere near THAT volatile. If you fill a small pan to, say, an inch deep with gasoline and let it sit (outdoors!) somewhere warm and sunny, you’ll see it will take quite a while for it to all evaporate away. Most alcohols and acetone, for example, are much more volatile than gas.
---
### Author:  [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)
#### Post date: [November 27, 2007, 5:58pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/17 "2007-11-27T17:58:11Z")
[QUOTE=Q.E.D.]
Gasoline is volatile, to be sure, but it’s nowhere near THAT volatile. If you fill a small pan to, say, an inch deep with gasoline and let it sit (outdoors!) somewhere warm and sunny, you’ll see it will take quite a while for it to all evaporate away. Most alcohols and acetone, for example, are much more volatile than gas.
[/QUOTE]
I know that. :smack:
I was still imagining the entire tank evaporating in less than a second, though. 😉
To reword the question, at what rate is fuel expected to be lost from the tank due to evaporation at a given temperature?
---
### Author:  [@Barbarian](https://boards.straightdope.com/u/Barbarian)
#### Post date: [November 27, 2007, 6:06pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/18 "2007-11-27T18:06:15Z")
[QUOTE=Q.E.D.]
1. Underground tanks have VERY little in the way of daily temperature swings. In any case, gas dispensers are temperature-compensated.
[/QUOTE]
There are [lawsuits pending](http://abcnews.go.com/GMA/Consumer/story?id=3022167&page=1) that say [that ain’t so.](http://www.nytimes.com/2006/12/15/business/15fuel.html?_r=1&oref=slogin)
---
### Author:  [@Sean\_Factotum](https://boards.straightdope.com/u/Sean_Factotum)
#### Post date: [November 27, 2007, 6:14pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/19 "2007-11-27T18:14:58Z")
[QUOTE=CookingWithGas]
What is the baseline temperature used to calibrate these? That is, at what temperature do you get a true gallon when the gauge indicates 1 gallon?
[/QUOTE]
I saw this in the paper this week down here in SE Virginia. The pumps in this state are calibrated to 60F.
---
### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [November 27, 2007, 6:37pm UTC](https://boards.straightdope.com/t/gas-pumping-tips-any-truth/427872/20 "2007-11-27T18:37:25Z")
[QUOTE=Mangosteen]
One of the most important tips is to fill up when your gas tank is HALF FULL or HALF EMPTY.
[/QUOTE]
Any idea on which of those options is the better one?
😉
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