When Warmer Temperatures Throw Off Gas Pumps, Consumers Pay

“In the summer time fuel gets hot and as the fuel gets hot the volume expands, but the energy does not,” says a new report from NPR. The basic idea is that while the volume of fuel expands and contracts, the amount of potential energy within the gas stays the same. A gallon of gas at 80 degrees won’t push a car as far as a gallon of gas at 60 degrees.

The difference is about 1%, enough to force wholesalers to sell “temperature adjusted” gas. If you gas is hot, the gas station owners get more of it for the same price. Not so with a gas pump. You pay the same for gas no matter what temperature it is.

NPR says the House of Representatives estimate you’re losing $2 billion dollars a year to expanded gas. Fuel companies say the winter months even it out. NPR also points out that “summer” gas (a different blend required by the EPA) actually has more energy per gallon…about 1-2% more.

Nevertheless, there’s a raging debate going on in several southern states about whether the nations gas station pumps should be retrofitted to adjust for temperature changes. If you’re lucky enough to live in Hawaii this doesn’t concern you; Hawaii is the only state to adjust for warmer gas.

Heat Throws Off Gas Pumps, and Motorists Pay [NPR]
(Photo: moorsteen)


Edit Your Comment

  1. mrmysterious says:

    This is all well and good, but all the gas station around me store their gas in underground tanks, so isn’t that temperature pretty consistent year round?

  2. j-o-h-n says:

    Will this stupid rumor EVER die!?!

    Yes, gasoline, like pretty much every liquid expands as the temp goes up — but the amount is so small you will never notice it!!!

    The reason gas formulations change by season is gas vaporizes easier at higher temps.

  3. alpha says:

    fill up in the morning and you’ll negate any warming (and thus expansion) that may occur.

    and J-O-H-N is right, the amount is quite small because liquids are relatively incompressible. I’d say you probably get cheated more by inaccurate (purposely) pumps than thermal expansion.

  4. mrestko says:

    I took physics a few years back and I rounded quite a bit when I was working through the problem. But I just went and found the record high and low temperatures for Chicago and the thermal expansion coefficient for gasoline. The difference in volume between 105ºF and -23ºF is only 0.07 gal (i.e. 7%). But you have to remember that those are unrealistic extremes since gas is stored underground and in actuality the difference would be so small as to be irrelevant.

  5. SonoranSam says:

    As we exchange email postings, the National Conference on Weights and Measures is meeting in Utah to discuss this very issue.

    Several states allow temperature compensation for wholesale fuel deliveries. As you note, Hawaii arbitrarily added a few cubic inches to a gallon of gas, a solution that only works there, where temperatures are uniform year-round.

    In hot weather states, gas pump temperatures can reach as high as 105 degrees in the current triple-digit heat. At that temperature, every consumer who buys 15 gallons of gas is losing about $1.30-$1.50 in lost energy.

    The oil industry hates automatic temperature compensation. They’ve been fighting it for decades – literally.

    Except for Canada, where in cold weather, consumers get more energy as gasoline contracts. In Canada, big oil think Automatic Temperature Compensation is a fine idea – and Canadian law mandates it.

    Ain’t that a coincidence?

  6. Jacquilynne says:

    Up in Canada — where the problem is mainly the opposite, that gas compression in longer winters would give consumers an advantage — we already have temperature adjusted gas pumps. Apparently yours is not the only government beholden to the gas companies.

  7. Jasmo says:

    well, seeing as we’ve been “victim” to this since, well, since we’ve been using gasoline in engines, isn’t it a little late to start griping?

  8. Chicago7 says:

    Hey, in the winter went it goes below freezing, the gas is denser then, right?

  9. nweaver says:

    THey temperature compensate the tankers because they swing in temperature ALOT and are dealing with large quantities.

    There is no point temperature compensating the pumps themselves, because the underground tanks are pretty constant in temperature year round.

    Some economist did the math: it would cost consumers MORE if you mandated temperature compensated gas pumps.

  10. swalve says:

    Just mandate that the weights and measures people calibrate the pumps in spring and fall.

  11. j-o-h-n says:

    The coefficient expansion for gasoline is about 0.00060 per degree (F). So after a 50 degree rise (60 to 110F) that would be (0.00060 * 50) = 3%.
    So if you pumped 20 gallons of 110F gas and in the morning it cooled back to 60F you would only have 19.4 gallons.

    But as has been mentioned, a giant underground tank of gas a) has a huge thermal mass and b) is pretty well insulated so it is very unlikely that you’d actually pump 110F gas. However this is good reason not to overfill your tank in the summer as you could lose some to expansion in your tank (a much smaller thermal mass which is not insulated).

    Of course, the opposite is true when the temp is below 60F – the gas is more dense.

  12. alpha says:

    oh math and science, how we do love thee.

  13. zolielo says:

    Repost? I think that I recall this topic.

    I recall doing the calculation and that the margin is trivial but for significant (100, 1000, etc.) of gallons i.e. fleet, RV, truck and boat.

  14. econobiker says:

    When the gas companies stop charging 9/10 of a cent then, and only then, should they NOT have to temperature adjust gas.

  15. Thrust says:

    Lets all throw ice cubes into our gas tanks, Weeeee!

    Up in Canadia we have temp-regulation on winter gas so we don’t rip off the pump, but never on summer gas. Me thinks we be takin it in the rump again.

    Smart buyers fill up at night, or early morning on the way to work.

  16. j-o-h-n says:

    @econobiker: Agreed. The 9/10 cent thing barely made sense when gas was 18.9c/gallon (about 1% off). At $2.999/gallon it’s just silly.

  17. doctor_cos wants you to remain calm says:

    It continues to be a marketing thing. $2.999 is NOT $3.00, even though it pretty much is.
    And funny how we’re told (again) that anything which might benefit the consumer (installing temperature compensation devices on pumps) would actually cost us more money.
    Record big oil profits are NOT CONNECTED with higher gas prices.
    Record high temperatures in the western US are NOT INDICATIVE of global warming.

  18. KenyG says:

    I thought most gas tanks were underground. When I fill up, the metal part of the nozzel is very cool to the touch, even on a hot day.

  19. jeff303 says:

    You gotta be kidding me… The House of Representatives? Let’s see their equations.

  20. Bryan Price says:

    And when you are living in say, Florida, where I only have to wear pants (versus shorts! Keep it clean!) maybe a couple of times per year, getting more fuel in the “winter”* to even things out doesn’t even things out.

    * I lived in Ohio, so I know about what real winter is.

  21. rhombopteryx says:

    Technically you get a _gallon_ of gas, regardless of temperature, so who’s being shotchanged??? If you were buying a certain mass of gas, or even buying a certain energy equivalent, that’d be different, but at least there’s no outright lying going on. (Yeah, this does suck – and Canada’s reverse situation proves it.)

  22. Elvisisdead says:

    You can’t swing a dead cat without hitting an MS or PhD on Capitol Hill. They’re called fellows, and damned near every committee has them. They’re acknowledged experts that help committees with subject matter when necessary.

    It would be like you buying a _gallon_ of milk at noon, and then once you chilled it down at home seeing that you were several ounces short.

  23. Mary says:

    Funny. Car Talk airs on NPR and they had a question regarding this (about if it was better to fill up in the morning or afternoon) and they said two things.

    1. Gas tanks are underground and the amount of gas that would actually be affected by the temperature is barely noticeable.

    2. The difference is so slight that you couldn’t possibly save enough money for it to actually matter.

    It makes sense to me. A lot more sense than paying thousands of dollars to regulate gas pumps even more, when there are a million and thirty two things about the whole industry that are much more important and fraudulent.