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Half full or half empty: winter storage and fuel

Winter is upon us, and for those living in cold-weather areas, this unfortunately means a season on the hard. Boaters who winterize are faced with a question: Should I fill my fuel tanks for winter storage or leave them empty? The answer has generated much debate.

A brief history of how fuels have evolved over the last half-century may help to shed some light on your choice. Several decades ago, the U.S. government began to focus on reducing our dependence on foreign oil.

Around the same time, emissions and greenhouse gas reductions became a national priority. Amendments to the Clean Air Act of 1963 imposed regulations on motor vehicle emissions, and the Energy Policy Act of 2005 introduced the concept of alternative fuels and non-petroleum-based replacements. As a result of this legislation, the fuel industry has experienced significant changes.

Two important changes include the removal of lead from gasoline and the reduction of sulfur in diesel. Methyl tertiary butyl ether and, later, ethanol replaced lead as the primary lubricity agent in gasoline. The introduction of biodiesel — a blend of renewable fuel and fossil fuel — accompanied the reduction of sulfur in diesel. Each of these changes resulted in cleaner-burning fuel, which reduced emissions, enhanced lubricity and increased combustion efficiency.

Original equipment manufacturers, mechanics and boat dealers, as well as the American Petroleum Institute, the Steel Tank Institute and other well-intentioned professionals, have offered widely differing opinions in the past on whether to leave tanks full or empty during storage, but recently they have come to the same conclusion.

Despite the benefits of evolving fuel chemistry, the introduction of water-absorbing renewable fuels to gasoline and diesel greatly reduces fuel stability during winter months and other periods of prolonged storage. Water is the primary enemy when it comes to maintaining fuel quality, promoting microbial growth and eventual fuel deterioration. In addition, the removal of lead and sulfur from previous fuel blends limits the control of microbial growth, as both are considered highly effective biocides, as well as lubricants.

What appears to be a complicated chemistry problem essentially boils down to a simple concept: Less surface area exposed within the tank and a smaller volume of air reduces the potential for condensation in today’s water-absorbing fuels. Experts in the fuel industry now recommend storing the tank at 90 percent of its capacity (the safe fill level) to minimize the potential for condensation and to allow for expansion. This protocol applies to fuel tanks of all shapes, sizes and composition.

In addition to a nearly full tank, it is also highly recommended that a stabilizer be added to the fuel prior to prolonged storage. The use of a stabilizer that effectively addresses water absorption can help to control microbial growth and extend the shelf life of fuel for 18 to 24 months. The increased lubricity and a boost to the octane/cetane will aid in maintaining fuel quality.

Water is public enemy No. 1 when it comes to maintaining fuel quality. Stabilization will only work when moisture is under control. Store the tank empty or full? Fill ’er up.

Tom Zarrella is co-owner of USA Fuel Service, a fuel polishing and fuel additive company.

See related article:

- Propulsion

January 2015 issue