Forget To "Winterize"
Your Fuel?

By Beth A. Leonard

With E10 gasoline, special care needs to be taken before storing it for the winter. But what if you didn't get around to it before the cold weather came?

Photo of various brand of fuel additives

Before ethanol, you didn't have to think too much about winter storage of your fuel. If you put a stabilizer in whenever you filled the tank, the gasoline would be fine come spring whether the tank was nearly full or nearly empty. But that's not true with E10 — gasoline with 10-percent ethanol in it. Since E10, manufacturers have strongly recommended either emptying the tanks completely or topping them up and adding stabilizer for the winter. So what would you do if you forgot?

Ethanol Plus Water Equals Problems

Ethanol is hydrophilic — it likes to absorb water. Water can get into your tank through leaks in the gaskets on the filler cap or from condensation inside the tank due to temperature changes. If water does get in, the ethanol in the gasoline will absorb it. That's acceptable with small amounts of water because it will simply be burned in the combustion cycle without harming anything. But ethanol can only absorb so much water. When it becomes completely saturated, phase separation occurs, and the corrosive ethanol-water mixture sinks to the bottom of the tank. If the engine is run, this mixture can damage seals, O-rings, injectors, and other delicate engine parts. The upper "gasoline" layer will be depleted of ethanol and have a reduced octane level, which can also cause engine problems.

The chances of phase separation happening increase if you leave the tank partially full in cold weather. With a full tank, there's no room for condensation to form so there should be no water for the ethanol to absorb. The more room there is in the tank, the more surface area there is for condensation formation and the less ethanol there is to absorb the resulting water. Cycling temperatures from warm to cold also increases the amount of condensation. Finally, ethanol cannot absorb as much water at low temperatures as it can when it's warmer, so the gasoline will phase separate sooner in colder temperatures (see chart below).

Once phase separation occurs, there is no way to reverse it. No additive can rejuvenate bad gasoline despite advertising claims to the contrary. Bad fuel is bad fuel, and the only options are to dispose of it or recondition it.

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