More of this Feature • Part 1: Oil Cooler • Part 2: Diesel Fuel Cleaning, Voltage Drop Test
Related Resources • Maintenance Q&A Index

I used a biocide to treat my diesel fuel but still wound up with a plugged fuel filter. Any suggestions? C.S., via e-mail
During long periods of fuel storage, the microorganisms that live and thrive at the water-fuel interface can grow into long strings and clumps. While you were right to treat your fuel with a biocide--I trust you checked with your engine manufacturer before choosing a product--you may have forgotten that once these microorganisms die, they settle to the bottom of the tank; biocide kills them but does not eliminate their carcasses. In fact, killing the bugs can worsen the problem by creating more bottom ooze that your fuel inlet will eventually pick up. The result can be a plugged filter, as it was in your case.

Repeatedly changing your fuel filters may eventually solve the problem--at first you may have to perform this kind of maintenance after each outing. However, if the accumulation is large, you have two options: One, have your fuel tanks cleaned with a portable filtering system. You should be able to find a company that does this in the Yellow Pages under "fuel treatment." Once the tank is clean, maintain cleanliness with regular applications of biocide, and keep an eye on your filters for a reoccurrence of the problem.

The other option is to install a fuel-polishing system on your boat that can continuously recirculate and filter your fuel, whether your boat is underway or at the dock. Some polishers rely on ultrafine filters, while others use a centrifuge or coalescer. Several companies manufacture such units, some of which are suitable for boats as small as 40 feet. Among them are Walker Engineering's AlgaeSep (818) 252-7788, www.walkerairsep.com; Belgoes Filtration Systems (866) 235-4637, www.fuelpolishing.com; and the Kaydon Filtration Group's Guardian System (706) 884-3041, www.cleanfuelinc.com. Prices range from about $1,300 to more than $4,000, excluding installation.

What is a voltage-drop test? A.V., via e-mail
A voltage-drop test measures resistance, the opposition to the flow of electricity, which can be caused by anything from normal wiring to a electrical malfunction. Basically the test uses a voltmeter to compare voltage at the beginning of a circuit to that at the end. If the meter shows no difference, there is no voltage drop. The greater the difference, the higher the voltage drop and therefore the more resistance in a circuit. Generally, voltage-drop readings of one or more volts are considered unsatisfactory. A voltage-drop test provides an excellent means of testing solenoids, battery cables, and high-current electrical leads.

When performing this type of test, always connect the voltmeter's red lead to the electrical source and the black lead to the electrical load.

Need help with a maintenance problem? Write to Maintenance Q & A, Power & Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax: (917) 256-2282. e-mail: ken_kreisler@primediamags.com. No phone calls, please.

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