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.

So What Do I Do Now?

Let's say you didn't know you shouldn't leave your tank half full for the winter or that you didn't get around to doing anything about it last fall, and now we're halfway through the winter. What are your options?

First you need to determine if there is water in the fuel. Pump a small amount out of the bottom of the tank into a glass jar or clear plastic bottle using a hand pump or a large baster (don't use an electric pump to do the job — a small spark can lead to an explosion). Let it sit for 10 or 15 minutes. If clear water or a cloudy layer settles out of the gasoline, then it has become contaminated with water. The cloudy layer consists of the mixture of ethanol and water that occurs with phase separation.

If you see no signs of water and the fuel appears close to colorless and smells normal, go ahead and top it off with fresh gasoline and then run it through your engine come spring. Before you do, change all the fuel filters as you would normally do when re-commissioning. Depending on your engine, that might include the in-line fuel filter(s) located between the tank and the engine, the onboard fuel filter, and the vapor separator tank filters. For small amounts of gasoline, it's worth pouring it through a coffee filter into a new container to be absolutely sure there are no contaminants before using it. If your engine shows any signs of hard starting or difficulty in running, dispose of the fuel, change the filters again, and switch to fresh gasoline.

Don't try using the gasoline if it shows signs of water contamination or phase separation. You can dispose of small amounts by taking it to your county's household hazardous waste collection site. Google your county and "household hazardous waste," and you'll find the relevant information. Most counties hold collections at least twice each year. Some counties recommend reconditioning old gasoline. If yours does, you will find information on how to do it on their website. For amounts over 10 gallons or so, your only option will be to pay your boatyard to dispose of it.

E-10 Seasonal Storage ChartClick on image to enlarge

And when it comes time to winterize the boat next year, don't forget about your gasoline. If you can't empty the tank completely, then top it off and add a good fuel stabilizer (one recommended by your engine manufacturer). Run the engine for 10 minutes to distribute the stabilized fuel through the engine and fuel lines. Make sure the seals in the filler cap are still intact, the cap is closed tightly, and the vent for the tank is not blocked. Then you can rest easy knowing that in the spring, your fuel will still be usable. 

This article was published in the Winter 2013 issue of Trailering Magazine.


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