Rick's Free Auto Repair Advice

Gasoline shelf life — How long does gasoline last?

How long does gasoline last?

Gasoline shelf life

There’s no set answer because it depends on storage conditions. But you want an answer anyway, right? Ok, when stored properly gasoline shelf life is 3 to 6-months according to some experts. Other experts same that ethanol blends start to go bad in as little as 30-days. Who’s right? Both. Read on to learn more about gasoline and what makes it go bad.

What makes gasoline go bad?

There is no such thing as pure gasoline. Gasoline is a blend of up to 150 different components and it’s formulated differently by every local/regional refiner to meet the needs of the local community where it’ll be used. The refiner varies the components and proportions based on the season (summer gas versus winter gas), altitude, and raw material prices. But all gasoline has one thing in common, it must vaporize quickly and ignite and burn in a controlled manner.

It’s the volatile components in gasoline that make it vaporize and burn and it’s those same volatile components that can affect gasoline’s shelf life if it’s not stored properly. So let’s take a look at what ages gasoline.

Air makes gasoline’s volatile components evaporate out of the mixture

Exposure to air is the #1 cause of gasoline degradation. Air exposure causes the volatile components in the gasoline to evaporate and leave the remaining mixture less able to vaporize and ignite.

Air makes the remaining components oxidize and turn to gum and varnish

Leave a glass of wine out on the counter for a week and see what’s left. The alcohol will be gone and the wine will be thick and gooey. The same thing happens to gasoline. As the volatile components evaporate, the remaining components oxidize, causing gum and varnish deposits that can clog the small passages in carburetors and fuel injectors.

Moisture in the air combines with the alcohol

Ethanol blends contain alcohol and alcohol is hygroscopic (absorbs moisture from the air). If the gasoline is stored in a vented gas tank, like on a small engine, it will absorb moisture in the air. After about 30-day in humid conditions, the ethanol blend will go through PHASE SEPARATION, where the alcohol/water will separate from the gasoline and fall to the bottom of the tank. From that point on, the engine will be supplied with the alcohol/water combination.

The storage container—plastic versus metal gas cans

Many gasoline storage containers are made from plastic, mainly polypropylene/polyethylene. Those containers allow some of the highly volatile components to pass through the plastic and evaporate. Metal gas cans don’t allow that passage, so gas stored in metal gas cans tends to last longer.

What is gas stabilizer?

Gas stabilizer contains chemicals that slow down phase separation, prevent gum, and prevent varnish formation. In addition, some fuel stabilizers contain a metal-deactivator ingredient that prevents metal oxidation in carburetors, fuel pumps, and fuel injectors.

When to add gas stabilizer

Add gas stabilizer at the pump when filling your gas can. That way it will fully mix with fresh gasoline and protect the gas right from the get-go.

How long does gas stabilizer last?

Some gas stabilizer manufacturers claim that gasoline stabilized with their product will last up to three years.

Can you add gas stabilizer to old gas?

You can, but it won’t do any good. Dead gasoline is dead. You can’t bring it back to life because all the volatile components are already gone and the rest of the gas has already turned to gum and varnish.

©, 2020 Rick Muscoplat


Posted on by Rick Muscoplat

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