Letter: Buying Gas for Storage

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Mr. Rawles,

I live where they switch between winter gas (Benzine, short molecule chains) and summer gas (pure, long molecule chains).

  1. Which is the best season to buy/rotate my gas supply for storage?
  2. Also, under normal circumstances premium octane is a waist of money or even bad for my machines, but is it better for storage?

God bless – B.

HJL Replies: In the past, JWR recommended buying fuel for long-term storage in winter months, because it had extra butane added (for cold weather starting) and hence it had a longer shelf life. However, since 2010 he has recommended buying storage gas in summer months, because ethanol is now added in winter months as an oxygenator, by Federal mandate. The problems created by this ethanol more than offset the advantages of the old winter gas formulations. Jim says that the ideal time to buy your gas each year is on or about May 5th, which is after the seasonal formulation change, but three weeks ahead of Memorial Day Weekend, when gas prices have consistently jumped. Look for a station that offers ethanol-free gas, and ask before you buy, to be certain.

Jim also recently mentioned that although the politics of ethanol are loathsome, he does recommend buying Flex Fuel vehicles with stainless steel gas tanks. These vehicles are compatible with ethanol mixes up to 85% (E85.)

Here are two links to articles about ethanol-treated gas:

https://www.consumerreports.org/cro/news/2013/03/gas-with-ethanol-can-make-small-engines-fail/index.htm

http://www.fuel-testers.com/expiration_of_ethanol_gas.html

In addition to these problems, ethanol has a nasty habit of attacking rubber, glues, and resins that are normally impervious to gasoline. Commercially-produced gas will also tend to have cellulose floating in it, which needs to be screened out by a good filter.

There are reports of E10 containing much higher amounts of ethanol (up to 35%) in some cases. (Though I couldn’t find any formal documentation of that.) Usually, this occurs from tanks of E10 gas separating, over time.

Also, stations that switch between the two have an additional problem. Normally, water and gas do not mix in a storage tank. The gas floats on top and the water settles to the bottom. When the E10 (or E15, E85, et cetera) is added to the tank, the company generally does not clean out the tank. They just add the new gas in. The ethanol will immediately begin picking up any moisture present in the tank. If enough water is present, then the entire tank of gas can be contaminated.

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