Question: When I took your one-day Introductory Diesel Maintenance Course several years ago, I forgot to ask one question: What is the best way to lay up a fuel tank for seasonal storage? For years now, I’ve been topping off my tanks when fall lay-up comes around in order to reduce the air space above the fuel and thus minimize algae growth. Just recently however, a marine professional told me that the fuel level makes no difference, primarily because the area of fuel-air interface remains the same whether the tank is topped off or not. He also said that topped-off fuel is likely to go stale over the winter.
Fort Myers, Florida
Professor Diesel: Most engine manufactures will recommend topping off your tanks as often as possible. The reason has more to do with the volume of air over the fuel than the area. The smaller the volume of air above the fuel, the less moisture there is to get into the fuel when temperature changes occur.
The so-called algae grows in water that finds its way into your fuel though many people refer to the stuff as bacteria, a practice that gives rise to many additives being called biocides. My own experience tells me that the more often you fill your tanks, the fewer problems you’ll have with algae or anything else. And climate conditions contribute to fuel deterioration, by the way. Boaters in Florida tend to have more problems with deterioration, for example, than boaters in less humid places like Maine.
Going with an additive is helpful, but be careful about which one you choose and don’t overdose. Some products have a very high ethanol or alcohol content, and this can reduce the lubricating value of diesel fuel and cause other problems, Moreover, your fuel hoses should be a serious source of concern when choosing an additive, especially if your powerplant is ten years old or older. Hoses may need to be changed because they are not compatible with a particular additive and/or biofuel.
Professor Diesel is Larry Berlin, director of Mack Boring’s Training Services division.
This article originally appeared in the March 2011 issue of Power & Motoryacht magazine.