Can I Safely Store My Boat

with 10% Ethanol (E-10) Gas

Now that Boaters and marine operators have had some time getting used to 10% Ethanol blended gasoline (E-10), we’ve put together some information on winter storage you may find helpful.

This gasoline is more apt to cause issues in boats than in automobiles due to the requirement that marine fuel tanks be vented. Ethanol is hydroscopic; it absorbs water out of the air that can enter a boat’s fuel tank through the vents. If enough condensation enters the tank and the boat is unused for long periods of time, such as during winter storage, the water can mix with the Ethanol and drop to the bottom of the tank forming a separate layer underneath. This process is called phase separation and it is a problem for boats manufactured prior to 1984. Why? Because when the water/Ethanol layer at the bottom of the tank rises to the level of the fuel pickup, it will be sucked up into the engine, shutting the engine down. The water/Ethanol layer WILL NOT support combustion. There is no quick fix. Once phase separation occurs, additives and water separators can't help; the only remedy is to have gasoline/ethanol/water professionally pumped from the tank.

The best practical recommendation learned from marina operators is to maintain a full tank of fuel with a fuel stabilizer added. Its best to add the stabilizer and a fuel treatment to the tank at the recommended dosage, run the engine for 10 minutes to allow the system to be cleaned, shut off the fuel valve to interrupt the fuel supply and allow the engine to run until it stops, topping off the tank until it's almost full to reduce the amount of exchange with the air that might bring in condensation. Do not cap the tank vent and do not fill with fuel to the point of overflowing. Some extra space should be maintained in the tank to allow for expansion and contraction of the fuel with temperature changes.

One product which comes highly recommended is Star Tron (manufactured by Starbrite). This additive is said to prevent and reverse E-10 ethanol enhanced gasoline problems. It also treats water in the fuel tank. REMEMBER – this helps with the fuel treatment & ethanol problem only, you will still need a good fuel conditioner or stabilizer when storing your boat.

MDR - a manufacturer of fuel additives - recommends this process:

1. Try to determine if there is any standing water/ethanol on the bottom of the tank. Check fuel filters, water/ separators, or use MDR's Water Probe Indicator (MDR-566) if the tank can be dipped straight down.

2. If no water is indicated, E-Zorb should be added at the suggested ratio of 1 oz to 20 gallons of E-10 gas to compensate for condensation during storage. If an excessive amount of water is indicated it should be safely pumped out and discarded according to local hazardous waste disposal methods. Then add an equal amount of E-Zorb to the remaining phased out water/ethanol on the bottom and agitate fuel (per "3" below). When the fuel clears all remaining water/ethanol has been emulsified back into the fuel (Fig. 3 above). Clear fuel can be determined by checking a fuel sample from the fuel filter or water separator after running the engine for a short time.

3. Now add MDR's Gas Stor-N-Start to the tank at a ratio of 1 oz to 5 gallons of gas with enough Stor-N-Start to treat the tank when totally full. Immediately thereafter fill the tank with fresh E-10 gasoline, which should be enough to agitate the E-Zorb and Stor-N-Start, dispersing them throughout the tank. However, if the tank is already full or only needs a small amount of new E-10 gas, insert an air hose to the bottom of the tank allowing the air pressure to bubble the gas for 5-10 minutes. This should be sufficient to complete the agitation process. Then, after running the engine for 5-10 minutes to circulate the treated fuel throughout the fuel system and lastly fogging the engine, the entire system is winterized and ready for Spring.

Draining fuel tanks of E-10 gas is dangerous and an impractical solution due to the possibility of gasoline vapor accumulating and being potentially explosive. Plus it is virtually impossible to remove all of the gas and phase separation could still occur with a small amount of fuel.

The worst choice, which was confirmed by marina owners in the Midwest, where they have been using blended gasoline for the past decade, is to leave the tank half-full over the winter. Tanks that are a quarter- to half- full breathe more and attract larger amounts of moisture.

Never try to plug up a fuel tank vent to prevent moist air from entering a tank. Boaters may be tempted to block tank vents to keep moisture rich air out of the tank. This isn't a good idea. Without room to expand, the additional pressure could rupture fuel system components.

. A partially full tank is not recommended because the void space above the fuel allows air movement that can bring in water through condensation as the air temperature moves up and down. This condensation could potentially become a problem.

Fiberglass tanks beware: Ethanol is known to chemically react with many fiberglass fuel tanks, which can cause them to deteriorate and potentially fail as it breaks down the resin that holds the fiberglass together. Unfortunately, unless your boat's manufacturer can confirm that your fiberglass tank was built to withstand ethanol, your only remedy may be to replace the tank with a non-reactive material such as aluminum.

Another issue with Ethanol is that it is a terrific cleaner. So all that gunk you may have built up in your tank over the years can be broken down and can clog filters, separators, and carburetors. It’s a good idea to keep several extra filters on board in the spring in case you need to change them when you’re out on the water.