In either case, you will have to make a decision on size and filter rating. Most filters used for fuel polishing are 10, 20 or 30 micron. The smaller the micron rating, the sooner it will clog – but it will also do a better job of cleaning the fuel. Decent-sized filters in the 10-micron range are most common.

Smaller filters use a replaceable metal filter canister similar to oil filters. Larger-capacity filters utilize a drop-in style filter element. Some filters come equipped with a see-through bowl, allowing you to check for water in the fuel. However, these don't belong in an engine room unless they are equipped with a metal bowl guard and are rated for use in engine spaces. Some filters can be equipped with electronic water sensors to alert you when they've collected excessive water.

WALBROThe Walbro FRA fuel pump is a new choice.The other key component in a fuel-polishing system is the pump. The pump should be certified for use with diesel fuel, be able to run continuously and have a low amp draw. The pumps are 12 volt D.C., so that the system can be operated while away from the dock. There are also 120-volt A.C. transfer pumps, but they are seldom used.

While one of the most common fuel pumps in the past was the Walbro 6000 series pump, Walbro recently discontinued it in favor of a new FR series of pumps. These pumps are available in a variety of capacities and configurations. They draw less than 2 amps at 12 volts, are reverse-polarity protected and can run dry for up to four hours. They are U.S. Coast Guard approved and can pump fuel continuously. Walbro can provide a variety of fuel-delivery volumes and pressures by configuring a core set of components. That means you can choose a pump more closely suited to your desired flow rates and pressures.

Other components required are two- or three-way valves, fuel-line parts and electrical parts. The valves need to be rated for use with diesel fuel. The fuel line also needs to carry Coast Guard certification for that purpose. In addition to the wiring and fuse or breaker for power, some systems utilize a timer to run the system periodically. Other systems run when the engine is on and have a simple manual on/off switch.

SYSTEM DESIGN CONSIDERATIONS

The simplest systems, used on single-tank installations, take the fuel from the bottom of the tank, pump it through the filter and return it to the tank. Boats with multiple fuel tanks require a bit more hardware to accomplish the task. Sometimes, a manifold is used to direct the fuel. Polishing systems for these more complicated systems should be designed so that fuel removed from one tank and polished is then returned to that same tank. Any other option could overfill a tank and cause a fuel spill.

Some diesel engines are equipped with a fuel-return line to return excess diesel, under pressure, back to the tank. Don't be tempted to direct this fuel through a filter and back to the tank as a quick-and-dirty polishing system. You risk overloading and damaging the engine fuel pump. The other problem is that this return fuel flow is simply too small to effectively circulate the content of even relatively small main fuel tanks.

WEST MARINERacor 500 series filters are stocked by suppliers.Draw out your proposed fuel-polishing system on paper before buying components and cutting hose. The old saying that a picture is worth a thousand words holds true in this instance. Accompanying this story are two diagrams of systems, from simple to complex. Study them, and then start designing a setup configured for your boat.

Make sure you have accounted for all fuel-distribution scenarios by tracing out the fuel-flow paths. Do the math to determine the size of the pump you will need and how long it will take your system to clean the fuel on your boat. Be sure to account for the power needed to run the polishing system, too. Perfecting the design at this stage saves you money and possible embarrassment. It also never hurts to consult a pro, or someone else who has installed such a system. Online forums like TheHullTruth.com are full of postings by boaters who have assembled and installed their own systems.

Next decide where you can install your system. It needs to be convenient to the fuel lines and tanks, to minimize hose runs and plumbing. It needs to be accessible so you can reach and easily change all the valve settings and replace filter elements. If it will go in the engine room, the filters need to have metal bowls or bowl guards to be legal. Fuel filters and valves need to be firmly mounted to withstand vibration and the stresses of opening and closing those valves.

In addition, rubber fuel lines need to be properly supported to eliminate chafing, rubbing or vibration that might loosen fittings and clamps. Consider mounting all the components on a piece of ¾-inch StarBoard polymer. Provide permanent labels for each valve, fuel line and filter. Also consider making a flow diagram part of the installation; future owners and surveyors will thank you.

Wiring should also be installed using American Boat and Yacht Council standards. That includes using yellow wire for the D.C. ground and providing a fuse or breaker in the power lines. Wiring should also be supported at least every 18 inches to avoid chafing. You can control the system with a timer, but consider sizing the system to allow continuous operation whenever the main engine is running. For example, a boat equipped with a 200-gallon diesel tank and a 20-gph, continuously rated fuel-polishing pump will turn over the contents of a full fuel tank every 10 hours. Aim for at least a couple of turns of the fuel per week, especially in the warm months, when microbes can explode. If you don't use your boat often, consider a higher-capacity polishing pump, or plan on running your system at the dock. At the current price of fuel, you don't want to risk losing a tank of diesel.