Protecting Your Boat from Ethanol Damage: Fuel Stabilizers and Winter Preparation

Proper winterizing of your boat’s fuel system and engine is essential when gasoline contains ethanol. Ethanol-blended fuels can absorb moisture and act as a solvent, leading to water accumulation, degraded fuel system components, clogged lines, and engine problems. Taking a few straightforward steps before seasonal storage and during the boating season can significantly reduce the risk of costly damage.

Why Ethanol Causes Problems

Two characteristics of ethanol create the most trouble in marine fuel systems. First, ethanol is hygroscopic—it attracts and retains water. Fuel that sits for long periods allows ethanol to collect moisture, which can settle in the tank and fuel lines. Second, ethanol works as a solvent. Over time it can loosen deposits, degraded rubber, or varnish inside older tanks and lines, carrying debris into the fuel system and up to the engine.

Use a Quality Fuel Stabilizer and Conditioner

Engine manufacturers and marine service professionals recommend treating fuel with a reliable stabilizer and conditioner before winter layup and periodically during the season. Stabilizers are formulated to inhibit corrosion and help prevent phase separation—the point at which ethanol has absorbed so much water that it separates from gasoline and forms a heavier ethanol/water layer at the bottom of the tank. This layer can be drawn into the fuel outlet and damage the engine.

Many boaters use products that target ethanol and remove carbon and varnish deposits. Examples include manufacturer-recommended formulas and specialty ethanol treatments and carbon cleaners. These additives are most effective when added to a tank and then circulated by running the engine long enough for treated fuel to flow through the entire system.

Tank Fill Strategies for Winter Storage

There are differing opinions about whether to leave fuel tanks empty, mostly empty, or nearly full for winter storage. Each approach has trade-offs:

• Empty or mostly empty tank: If fuel is removed, ethanol cannot absorb water or loosen internal deposits in the tank. However, an empty tank can allow condensation and oxygen exposure that increase corrosion risk.
• Topped-off tank with treated fuel: Filling the tank nearly full reduces the air space where condensation and moisture can form and minimizes flammable vapors. It also reduces the chance of phase separation forming at the tank’s bottom. Topping off is recommended for larger tanks and by many safety organizations to limit explosive fumes.

For small tanks (roughly up to 40 gallons), draining and storing fresh treated fuel separately may be practical. For larger tanks, treating and filling the tank before storage is generally the safer and more convenient option.

Fuel System and Engine Maintenance

Beyond treating the fuel, inspect and service components that directly affect reliability:

• Drain and replace the fuel/water separator and any inline fuel filters.
• Drain carburetors or vapor separator tanks if your engine design includes them and if the manufacturer recommends doing so after circulating stabilized fuel.
• Inspect and replace deteriorated fuel hoses, fittings, and primer bulbs with ethanol-resistant materials where needed.

Simple Test for Ethanol Damage

A quick, practical test can reveal whether ethanol has already affected your fuel system. When changing the fuel/water separator, pour some of the drained gasoline into a clear jar and let it settle. Look for water, sediment, and black flecks. Black specks often indicate internal deterioration of rubber fuel lines or other components. If you find such debris, replace the compromised hoses and fittings with ethanol-resistant alternatives and thoroughly clean the system.

Filters, Micron Ratings, and Change Intervals

Water/fuel separators and filters protect the engine by catching debris and moisture before fuel reaches sensitive components. Experts typically recommend filters with a 10-micron rating for marine use and advise changing filters every 50 to 100 hours of operation and again for winter layup. Regular filter changes, combined with stabilized fuel, lower the risk of clogs and engine damage.

Practical Winterization Checklist

• Add a quality ethanol-focused fuel stabilizer and conditioner to the tank before layup.
• Run the engine long enough to circulate treated fuel through the system.
• Consider adding a carbon-cleaning treatment to remove gum and varnish during the season and before storage.
• Decide on a tank fill strategy based on tank size and storage conditions—either drain small tanks or top off larger tanks with treated fuel.
• Replace fuel/water separators and inline filters; inspect and replace hoses and fittings as needed.
• Perform the jar test when changing separators to check for water and debris.

Taking these preventative steps helps protect your fuel system and engine from the unique challenges posed by ethanol-blended gasoline. Regular use of stabilizers and cleaners during the season, combined with careful winterization, will reduce the likelihood of deposit buildup, water ingress, and component degradation.

This article originally appeared in the December 2010 issue.