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What’s the shelf life of Gasoline?

What’s the shelf life of Gasoline?

Curiously, not much thought is given to how long gasoline lasts. Gas pumps show us the price per gallon but have you ever noticed a “best when used before” date on the pump next to the octane rating?You probably haven’t, since it doesn’t exist.However, there is an expiration date on gas.So how do we determine what that is?Just how long does gas last and what happens if it’s met its expiration date?

One component (which are many) of gasoline is Ethanol.It’s a major additive and accounts for up to 10% of the volume.Ethanol is hydrophilic, this means it likes water and draws water in through moist, humid environments; basements, sheds, semi-outdoor spaces like car ports or anywhere near bodies of water like lakes, streams or oceans.If gasoline is stored in a humid area, or actually most areas it absorbs water.In large amounts it becomes a problem, and can prevent a car from starting and can damage internal fuel and engine parts.

Other compounds in gasoline, commonly referred to as “light ends”, are light hydrocarbons that volatize and evaporate.It’s these compounds which start the engine.Over time these compounds get evaporated out and can be one the reasons a car with old gasoline won’t start.

The last but most serious condition of old gasoline is oxidation.
Hydrocarbons called olefins have a chemical structure which particularly attracts oxygen.Once this happens the gasoline develops a gum like film.When gasoline sits for a period of time the film eventually solidifies into a gum-like polymer.These polymers don’t burn well, can gum up important fuel system components and can cause damage to the engine as well.

So how can you tell if gasoline is old and has gone bad?Here are three tips:

  1. Smell it; if it’s bad it will smell like rotten milk or a moldy gym sock.
  2. Check the color; it should have a greenish yellow appearance not a muddy orange tint.
  3. If the gasoline is stored outside your vehicle you will be able to spot the gum build-up.

All in all, gasoline should last about 6 months if kept in ideal conditions and could exceed that time by double if a fuel stabilizer is used.

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