Features January 2014 Issue

Diesel Fuel System Maintenance Best Practices

Donít 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 itís 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 canít 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 wonít 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), donít 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 doesnít run if the car is recharged often, they took steps to make sure stale fuel wouldnít 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 donít 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, ďmaintenance mode,Ē and we think thatĎs a healthy way to look at it.

Comments (3)

Simple tank fill advice from an old fuel oil delivery guy - when filling your boat diesel tank listen to the sound coming from the tank vent, it is attached directly to your tank. The fueling sound will change when the tank fills and and fuel enters the vent line. Stop then. Don't leave fuel sitting in your fill hose in the off-season.

Posted by: Waterman | February 12, 2019 7:10 PM    Report this comment

Very informative article!. I have a question. I am restoring a deisel power sailboat, which I winterized approximately 1 yr ago. I topped off the fuel tank and added Biobor for growth retardant. I do not plan on having the project completed till Summer, 2019. I am out of the water on stands. Do you recommend that I run engine with hose and rewinterize?

Posted by: itaylor4u | December 22, 2018 5:46 PM    Report this comment

You can fill the tank too full. Last season I filled my diesel tanks to the very top. All was fine until a bright sunny day mid-winter when I noticed a strong diesel smell from outside the boat. I finally traced it to the diesel fuel vent on the sunny side which was burping diesel. I siphoned off about 5 gallons of fuel at the deck plate, before it stopped. As the seasons turned and the sun fell on the other side of the boat, it happened again. (I cleaned it up with ethanol).

The issue is how does one tell when the tanks are full enough. My Maretron gauges are not sensitive enough. A site glass would be a simple solution but I am not sure how it could be used safely on a boat. I wonder how others have solved this problem. Overfilling is a problem even for a regular boating season fills.

Posted by: RRow | December 20, 2018 10:41 AM    Report this comment

New to Practical Sailor?
Register for Free!

Already Registered?
Log In