Gasoline savings

There’s one of those rapidly spreading quotations circulating on the Internet. Here’s the full text with some comments reflecting my skepticism about the arguments following it.

Tricks to get your money’s worth

TIPS ON PUMPING GAS–GOOD INFO I don’t know what you guys are paying for gasoline….Here in California we are also paying higher, up to $3.50 per gallon. But my line of work is in petroleum for about 31 years now, so here are some tricks to get more of your money’s worth for every gallon..

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 is actually 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.

Hope this will help you get the most value for your money.

The seems a bit bogus to me. Here are some concerns:

  1. First off, as StarrHillGirl pointed out in private correspondence, this argument sounds like it’s mostly about saving $$, but it tugs at one because it also has a little altruistic, save-the-Earth feature to it. That’s a problem-some misdirection argument.
  2. The morning cold idea seems bogus. Underground temps don’t vary much. Caves stay 55 (F) pretty much constantly, once one gets below the freeze-thaw depth of–what?–12-18 inches.
  3. The pump handles have the shut-off valve that operates on the basis of the vapor feedback. When the gasoline vapors start coming back up the filler neck from the tank, the pump stops. If the quantity of vapor differs, it’s going to be the quantity in the neck, and that’s gonna be a pipe of pretty narrow diameter and only a couple of feet in length.
  4. The overall differences that these reasons would account for are bound to be tiny. To create a careful test, any experiment to examine the ideas would require tremendous control (no variation in acceleration rates per tank of gasoline; driving on consistent road surfaces and switching tires with each fill-up to keep friction the same; statistical covariation to correct for differences in the amount of time one drove into versus with winds; correction for the proportion of time one was driving in the draft from vehicles in front of one) or huge numbers of cars and tanks of gasoline per participating car.
  5. The Mikklesons, of Snopes.com, don’t yet have a review, but the origin of the idea is under investigation.

So, I’m pretty skeptical. Perhaps I’m way off base and someone who knows a lot more physics than I can set me straight. If I’m uninformed, please explain in comments. If there are other reasons to doubt this explanation, please drop them in the comments, too.

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1 Comment

Filed under Amusements, News, Notes and comments, Science, Skepticism, Technology

One response to “Gasoline savings

  1. Kristy Welsh

    Most of these ideas run the along the lines of urban myths. Here is a pretty good article that uses EPA factors of evaporation:

    http://www.creditinfocenter.com/wordpress/2008/07/24/increase-mileage-gas-tank-full-or-half-empty/

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