Dont look to tank vent filters and fuel additives to solve real fuel-system problems. They are only ancillaries to regular fuel system-management and maintenance, improving reliability even further. Here are some fuel-system management best practices that we recommend.
- Buy diesel from the busiest fuel dock, preferably one that serves commercial users. A busy service station is good, too.
- Eliminate outside free water. Inspect the tank-fill opening annually, and replace the O-ring as needed. A little Vaseline can help with sealing and can prevent seizing. To keep water from splashing in the vent or from being forced in by a following wave, install a high loop in the vent hose, at least 12 inches above the tank, and consider a P-trap, if the function is questionable.
- Keep the tank full. This is vital with gasoline tanks, but its also important with diesel. Tank breathing is proportional to the free space in the tank, and a tank that is kept 90-percent full simply cant absorb significant water through breathing. Some like to keep only the minimum amount of fuel in the tank, with the false belief that they can keep the fuel fresh in this way; however, this practice dramatically increases both humidity and oxygen exposure.
- A diesel fuel-polishing system designed to recycle and filter the oil is a good idea. There always will be some sludge in tanks, and often, there will be some biological growth. Frequent filtering won't stop these things, but it will keep them manageable and reduce surprises. Most of the bacterial and fungal spores will be removed along with bacterial debris, reducing growth.
- Some believe in continuous biocide treatments. Some rely on dry fuel and filtration. If you do chose biocides (PS, July 2009), don't wait until things are bad; treat at the first sign, when there is any slimy dirt on the primary fuel filter.
- Applicable to both gasoline and diesel systems, fuel/water separators and high-capacity filters deliver valuable protection should you get a bad batch of fuel or when rough weather stirs something up.
- Use your engine. Many sailors pride themselves on running the engine just enough to clear the marina. The problem is that the engine never really warms up, so only a fraction of a gallon is used each trip, and the fuel stays in the tanks for a year or longer. Neither gasoline nor diesel is formulated for that sort of long-term storage. Except for long-distance cruisers, most sailboat engines die from disuse, not wear.
An interesting note: When General Motors came out with the Chevy Volt, which includes a small back-up engine that doesnt run if the car is recharged often, they took steps to make sure stale fuel wouldn't be a problem. The tank is completely sealed, without a working vent. It is designed to simply withstand the pressure, eliminating evaporation and all water and oxygen entry. And, if you don't burn enough gas, the computer warns you, then simply starts running the engine generator instead of using battery power; the intent is to keep the engine lubricated and to insure fuel turnover, never permitting gasoline to sit for over one year. The display announces, maintenance mode, and we think thats a healthy way to look at it.