Fuels for storage: Good, better, best | Fuel Facts

Photography Credit: Eddie Jones/Unsplash

Winter sends many classics into long-term storage. How well those cars emerge from stasis, however, can depend on the fuel in the tank. 

[What really happens to a car when its gasoline sits?]

Good: Premium Unleaded

“A premium pump gas will be made of a larger percentage of higher-octane components,” explains Zachary Santner, technical specialist with Sunoco Race Fuels. He adds that higher-octane components have a longer shelf life than lower-octane components. Lower-octane fuels–like 87 octane–contain the low-octane hydrocarbons that refineries need to get rid of. “In most cases this isn’t an issue because the fuel is used up in less than a month and there isn’t enough time for varnish and gum to form in the fuel system,” he continues. 

Better: Ethanol-Free Fuel

An ethanol-free fuel, available at select stations, can prevent water from sneaking its way into the fuel system. “Ethanol is hygroscopic, which means it can absorb water out of humid air,” Santner explains. “If a fuel system isn’t totally sealed, it will breathe as daily temperatures rise and fall, which will bring water vapor into the open space of the system. During storage, this can transfer a considerable amount of water into the fuel system, where corrosion can begin.” 

Best: Dedicated Storage Fuels

Such creatures do exist. “A storage fuel like Sunoco Optima is designed with all of the above taken into account,” Santner explains. “Optima contains no ethanol and is extremely stable, which prevents water intrusion and oxidation, respectively. The fuel is specially formulated to fight varnish formation by having a gum content that is 10 times lower than allowed in pump gas.” This 95-octane fuel remains stable for at least three years, he adds.

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Bardan New Reader
6/25/21 10:55 a.m.

Good, short, straightforward info, but you left out aviation fuel that has a long storage life. I'm still amazed at how many collectors whine at the price of specialty fuels, yet don't consider the damage to the fuel system that pump gas can do. The fact is collector cars don't use enough fuel in the course of a year to be a significant cost.

David S. Wallens
David S. Wallens Editorial Director
7/1/21 10:16 a.m.

In reply to Bardan :

Thank you. We actually covered aviation gas in its own piece: Why Not Avgas in Your Car? While it doesn't contain ethanol, our expert at Sunoco cautions that avgas contains some unnecessary additives. 

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