27 December 2012

Tips on getting gas for your vehicle


Confirmed at Wikihow -
And a link there led me to this tip at Life123:
You learn something every day.


  1. With all due respect I feel this post is somewhat in error or more clearly stated somewhat true but more internet hype. First, underground tanks today are 1) underground, where temperatures are near constant 2)double fiberglass tanked adding insulation to the stable ground temperature. Therefore time of day means little in regard to thermal expansion of gasoline stored underground.
    Not pumping when the tanker truck is discharging and stirring up the tanks sediment/water is likely a good idea.
    Slow pumping to reduce vaporization creates more time for vaporization likely equalizing the shorter time and higher rate of fastest pump setting. Besides, the amount of vaporized liquid on a 20 gal fill is negligible, slow or fast fill. Many pump nozzles have vapor reclaimer to prevent vapors from entering atmosphere.
    I found this comment on a 'thermal expansion of gasoline' blog which I feel is most accurate and helpful:

    From a first principles perspective, this seems possible but from a statistical perspective it seems like internet hype with a kernel of truth.

    First, some newer gas pumps use a temperature corrected flow meter that doesn't have this problem. Drewsser-Wayne shows the following flow meter corrector for use in europe: http://www.wayne.com/internet/busine...ure/atc_eu.pdf

    A bit of googling leads me to NIST Handbook 44 which says that the accuracy for a gas pump should be within 0.5% at 60F.

    SeeTable T.2. Accuracy Classes for Liquid Measuring Devices Covered in NIST Handbook 44 Section 3.30 on pg 3-15 of the following reference.


    This means that a 20 Gallon fillup could have an error of .1 gallon or about 375 ml due to intrinsic pump accuracy plus thermal error.

    According to the article cited by lugnet the thermal error for gasoline dispensed at 85F for a 20 gallon fillup is about 0.3 gallons.

    The worst the result could be on a 20 gal fillup is plus or minus 0.4 gallons, .3 from temperature and .1 from pump accuracy. If we assume that temperature is normally distributed, that the gasoline dispensed has temperature with average of 60 degrees plus or minus 25 , that the temp expansion of gas is linear at the same rate above and below 60 (not actually true but close) and we also assume that the average pump error is 0 with a standard deviation of .1, propagating errors gets us that an average 20 gallon delivery at a random time during the year will be 20 gallons plus or minus .3 gallons. Thus intrinsic pump accuracy is fairly irrelevant in this case.

    I submit the following argument:
    Since weights and measures folks don't like short deliveries and punish for them, that eliminates most short deliveries. Since most of us live in a temperate climate, we benefit from cold deliveries and lose in hot deliveries.

    Since most of us buy gas year round and weights and measures folks have eliminated most of the short deliveries, we are likely on average during the course of a year to get more gas than we paid for.

    In short, if you buy one tank a year and it's July 4th after the gas truck has driven 8000miles from Armpit, TX where it's 85F and filled the station with hot gas then you will get shorted. If you buy gas every couple weeks like most of us then the temperature effect averages out to no net effect over the course of the year. Source: http://bbs.homeshopmachinist.net/threads/28237-thermal-expansion-of-gasoline

    1. I agree. I've never given much credence to the thermal expansion claims, which is why I didn't copy them into my post.

  2. I am going to chime in and call shenanigans on the sediment issue. I'll agree that filling the station tanks may churn up the gunk. But any reputable gas station filters their fuel prior to dispensing it. They would be liable for the damage to your car if they didn't. In the Milwaukee area this fall a station put the wrong gas into (i believe the Premium tank) and damaged cars, they paid for the repairs to those engines and I am sure it was not cheap. And if for some reason they don't your car also has a fuel filter in it to prevent anything from getting past it to the engine. That is also why the myth that says "Don't run your cars tank to empty because it will cause it to suck the crud at the bottom of the tank" is also false. Because it is filtered before it is ever sent to your engine. Your vehicle will have "Change Fuel Filter" on it's scheduled maint. list (at least all older vehicles did).
    Not to mention that a moderately busy station has it's tanks re-filled almost every other day. Multiply this station re-fill event by the number of stations in this country and then cross reference to how often you have heard someone wrecking an engine from the sediment from a station. It is a non-issue.

  3. You can pump your own gas here in Oregon if you're on a motorcycle. The attendant has to hand you the nozzle and reset the pump, and run your credit card through the reader. When you're done you're supposed to hand the nozzle back to the attendant, but if there isn't one close by I just replace it myself. I've never been called on it in the 23 years I've lived here.

    I'm not certain if this is written into law, but it's a universal practice. I once asked an attendant why there was an exception for motorcyclists, and he said nobody wanted to be responsible for spilling gas on a custom-painted surface or a hot engine. It's as good a reason as any.

  4. I never could figure out how to set the handle to pump without my holding on to it. I remember when I was a kid and they had attendants to pump your petrol for you, and they'd set it to go and while it was pumping they'd wash your windscreen, check your oil and your tyres. But since I've been driving, nobody's ever shown me how to set the handle myself. Guess I should ask someone one day!

    1. Some pumps have little hinged levers that can be set to hold the squeeze handle. I see less and less of such levers as the years go by.


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