PS Advisor November 2006 Issue

Cleaning Fuel Tanks

I own a 22-year-old, 38-foot sloop. I would like to see a report on fuel tank cleaning and maintenance, including an analysis of additives. In my case, the tank can’t be removed and has no inspection port, so I am looking for systems that will do the job with the tank in place.

Jim and Loy Norris
Pearson 386, Lakota
Centerport, N.Y.

Let’s begin by dispelling any myths concerning “touchless” tank cleaning. A seriously, or even mildly, contaminated fuel tank can be properly and completely cleaned only by gaining access to its inside. Additives may help prevent some contaminant build-up, however, no additive will remove years of accumulated organic- or mineral-based sediment or water. Organic contaminants include biological lifeforms—both living and dead (when they die during cold weather or when you treat the tank with a biocide, their carcasses sink to the tank bottom, where they remain until they’re pumped into your fuel filters or are removed). Mineral-based debris includes asphaltine, which is essentially a tar-like, mineral-based substance that passes through the refining process or is accumulated in transport and storage facilities before it ever reaches your boat’s fuel tank. Contrary to the claims of many additive makers, it is nearly impossible to remove large amounts of any of these contaminants with a few caps of a silver-bullet additive.

However, it is possible to limit contamination with the use of additives. A biocide such as BioBor can help to control or limit biological growth. But every time you shock or treat the tank, the bodies of what you kill will accumulate in the nether regions of the tank. No additive will dissolve their skeletons, which are abrasive and harmful to your engine’s fuel system. Contrary to popular belief, the biological life that often thrives with a diesel fuel tank is bacterial; it’s NOT algae. Algae require light to carry out photosynthesis, and there’s not much of it in your fuel tank.

Too much of a good thing can be harmful: Biocides, if overused, can be corrosive and damage your metallic tank or other fuel system components. The best way to stem biological growth is to keep water out of the tank by using a stripper tube (this will be discussed in our upcom-ing report on replacing fuel tanks). Without water, the bio-life forms have nowhere to live.

As the fuel remains in your tank for long periods, the lighter, aromatic components will evaporate, albeit slowly. As this occurs, the heavier components, or “ends,” remain. These heavier molecules will begin to attach themselves to each other, collect, and then sink to the bottom, where they will accumulate and become part of the asphaltine base. Additives such as PriD are available to replace these lost aromatics, but knowing how much to add is tricky.

If you want to be certain that your tank is clean, the best and only sure way to do it is to get inside the tank. It’s not as difficult as it sounds: Access plate kits are available. One, manufactured by Sea Built Inc.,, comes in several sizes; these can be installed on the tank top or side by a skilled do-it-yourselfer or your favorite boatyard. Once the inside is accessible, cleanup can vary from light duty swabbing with a lint-free rag (never use “shedding” paper-based products), to the heavy-duty, requiring mechanical abrasion with paint scrapers, gasket removers, brushes, and solvent.

How often you’ll have to do this chore depends on the quality of fuel you take aboard. Poor-quality fuel will increase the frequency of this event, while careful fuel dock discretion or funnel filtering may mean you’ll only be seeing the inside of your tank with each presidential election, and what better time to be cleaning up dirt, debris, and detritus?


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