Reduce Gasoline Evaporation in Boats with These Tips


Gasoline samples

Sometimes it is not what has been added to your fuel that matters, but what is missing. The most obvious difference between gasoline and diesel during our vented, fuel-aging tests was that gasoline samples evaporated and required replenishment at the mid-way point; diesel samples did not. Studies by BoatUS and the U.S. Environmental Protection Agency (EPA) have shown that anywhere between 5 and 20 percent of the contents of a portable or installed polyethylene gas tank can vanish in one year through evaporation and permeation. The remaining fuel is lower in octane, contains fewer of the volatiles that are so essential for easy starting, and has reduced solvency for gum and varnish. It often looks perfectly good-most of our samples did-but it is perfectly rotten and potentially harmful as fuel.

There are several things you can do to ensure that fuel doesn’t go bad during periods of long-term storage.

Reduce permeation: New EPA requirements for low-permeation jerry cans, plastic tanks, and hoses are a blessing. The loss of vital volatile material is reduced, and odors are reduced. However, our experience with the new jerry cans and portable tanks has been disappointing. Most of the designs weve tried have serious flaws; we can only hope the market place will sort that out. Metal tanks have zero permeation.

Store in a cool place: Keep jerry cans out of the sun whenever possible.

Vent filters: The EPA mandated carbon filters on new boats, and aftermarket silica-gel filters reduce water absorption and reduce tank-breathing losses. Over their typical 10-year life, these filters can pay for themselves in saved fuel alone before factoring in reduced engine problems caused by corrosion and varnish. (Depending on the boat, you can expect to save 1 to 3 gallons per year.) (See PS January 2013 and PS January 2014.)

Keep the tank full: A full tank does not breath, and fresh fuel renews the volatile content.

Keep the vent closed when not in use (dinghy engines only): Water absorption and evaporation affect small tanks more quickly.

Run the engine often: The silence of wind power is nice, but gas does not keep.

Practical Sailor has been independently testing and reporting on marine products for serious sailors for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising or any form of compensation from manufacturers whose products we test. Testing is carried out by a team of experts from a wide range of fields including marine electronics, marine safety, marine surveying, sailboat rigging, sailmaking, engineering, ocean sailing, sailboat racing, and sailboat construction and design. This diversity of expertise allows us to carry out in-depth, objective evaluation of virtually every product available to serious sailors. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser with more than three decades of experience as a marine writer, photographer, boat captain, and product tester. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.


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