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. 

cbcleland New Reader
11/10/21 3:01 p.m.

I know we are talking about storage fuels but the owner of that Z car should also consider a good cleaning before putting it to bed!

RadBarchetta New Reader
11/11/21 7:39 a.m.

I'd like to hear more about the effects of ethanol on water contamination. I'm starting to see more and more claims that, while ethanol isn't so great for other reasons, water contamination isn't one of them, and that it may actually be advantageous. Also the claim that ethanol "absorbs water out of the air" is not true. The primary mechanism for water in fuel is from condensation in the fuel tank.



This one is particularly interesting, since it shows how water reacts to gasoline with and without ethanol.


11/11/21 12:03 p.m.

I've heard pros and cons about Stabil.  What do you think?

murphmi New Reader
11/11/21 3:18 p.m.

In reply to rhart6 :

Yes, someone please answer the question-- does Stabil really work, or is it all a marketing ploy? I've used it a few times but admit that most of the time I don't and haven't had a problem yet that I know of. For my TR-6, I try to remember to fill the tank with premium to leave a minimum amount of air at the top of the tank. But I keep the car ready to go, and will use it occasionally in the winter when there's no snow/salt on the road here in New England. 

I don't use Stabil in my lawnmowers, snowblowers, or boat (tho after running the boat I always shut off the fuel supply and run the engine out of gas to minimize varnish and gum buildup. Haven't ever had a starting problem (yet). Last week I started the 35- y.o. snowblower with last year's fuel still in it--started on the second pull. 

8/26/22 9:35 a.m.

For cars without catalytic converters, you can use Sunoco Surge. Has some lead. 

David S. Wallens
David S. Wallens Editorial Director
9/13/22 10:50 a.m.

So, what's in StaBil and does it work?

Let's go to the safety data sheet, the document that tells all.

What's a safety data sheet? It's a standardized doc that, in theory, tells all about a chemical compound. You can read a bit more about them here: Do fuel additives actually work? | Fuel Tips.

Section 3 of the SDS will list the ingredients. 

You can usually find the SDS via some googling. If there's a spill, ingestion or other emergency, those involved will need that info asap. 

So, I found this one for StaBil.

For helping on breaking down the details, see if this helps: Fuel Tips: Antioxidants, Fuel Stabilizers, and You

The TL;DR: There are antioxidants in StaBil, and that's good for your gasoline. 

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