ArticleService Repair

Fuel Filters

If there ever was a boating application that manifested the axiom that “an ounce of prevention is worth a pound of cure,” it’s installing high quality fuel filters. With the proliferation of E-10 gasoline and bio-diesel in coastal marinas, and the potential of even more radical changes to come, the importance of having effective fuel filtration between your vessel’s tanks and engines has never been greater.


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A clear bowl with built-in water drain for removing visible contaminants has become the standard in modern fuel filters.

E-10 gasoline brings a dark side to the marine fuel mix. The alcohol-laced gasoline cleans out all of the muck in your boat’s tank and fuel lines and transports it directly to your engine, where it can cause a world of hurt by restricting fuel flow, starving engines for fuel under high-speed loads, and causing premature overheating and powerhead failure. Another problem with E-10 fuel is phase separation, a situation where moisture introduced into the fuel supply causes the ethyl alcohol to chemically delink from the petroleum and settle to the bottom of your tank(s) where your pickup feeds are located. Phase separation creates bad chemistry that will ruin your day if your engine runs on it for an extended period. Adding an in-line fuel filter between your boat’s fuel tank and the outboard engine(s) should help minimize these two problems.

If you only have one filter on board, it’s best to go with the 2-micron element that will catch just about everything.

On the diesel side, B20 biofuel and other biofuel blends are starting to make their way into the marketplace. B20 derives its name from a mix of 80 percent diesel and 20 percent biomass and like E-10 and E-85 gasoline, its intent is to use renewable domestic resources to produce a fuel that reduces our dependency on foreign oil, while also limiting greenhouse gases. With the introduction of B20 into the diesel fuel equation, it’s more important than ever to trap contaminants and water before they reach your engine and cause problems.

To get the latest intel on fuel filters, I called a trio of experts from Mercury, Yamaha and Racor. David Meeler is the Marine Product Information Manager for Yamaha and recommends using a 10-micron fuel filter between the tank and the engine, since it’s “the primary line of defense and helps protect all of the onboard filters behind it.”

A typical F225 V6 four-stroke outboard has four additional fuel filters on the engine, with a small in-line filter/water separator on the fuel intake line with a red ring water indicator that must be changed every 100 hours, a filter/screen at the bottom of the vapor separator tank that should be changed every 200 hours, an in-line fuel filter between the fuel pump and the fuel rail that should be replaced every 100 hours, plus screens at the base of each fuel injector that are only serviceable by the dealer.

Yamaha offers two different 10-micron filters, with the mini slated for outboards up to 115 HP and a standard filter for every outboard in the Yamaha arsenal up to 350 HP with a flow rate of 90 gallons per hour. The “Big 10” offers 95 percent efficiency and Dave recommends changing the replaceable canister element every 50 hours. If you have a Yamaha outboard with Command Link, there is the capacity for this system to identify water-in-fuel problems via electronic sensors.

My next call went to John Neville, Director of Service Parts for Mercury Marine. The latest addition to their family of fuel filtration products is their High Capacity Water Separating Fuel Filter, which is an enclosed spin-on canister type that offers a 16 oz. internal capacity, which is twice what most competitive aftermarket filters offer. This newbie offers 10-micron filtration at 90 percent efficiency with a flow rate of 120 gph. Because of its added volume, the recommended change-out interval is 200 hours. According to John, this filter is offered with both Quicksilver and Mercury branding, and offers a specially engineered silicone media that strips water more efficiently out of ethanol-based fuels. The Merc High-Cap is good for both gas (E-10 max) and diesel (up to 7 percent biodiesel) applications. It contains 25 percent more media than comparable aftermarket filters for longer life. Its low-pressure drop reduces fuel flow restriction, helping to prevent vapor locking and stalling, and the internal epoxy coating protects against corrosion.

A secondary issue for fuel filters is the need to keep the vacuum between the tank and engine within specs. As the fuel filter clogs and cuts off flow, vacuum increases as it takes more effort to pull fuel through the system. This causes premature wear on the fuel pump and its components and leads to vapor lock. John recommended that boaters use a vacuum gauge on the engine inlet with a T connection and monitor the vacuum pressure.

Yet another fuel filter offered by Mercury/Quicksilver is one that was developed by the engineers at Parker/Racor. The model S3227 10-micron replaceable element is essentially married to a standard Racor 320R-RAC-01 frame with a clear bowl that features a built-in water drain to remove visible contaminants. The replacement elements are available through local marine retailers and also come with an optional electronic water-in-fuel sensor.

Speaking of Racor, no article on marine fuel filtration would be complete without talking to the folks that practically invented the game. Mark Dickman, Racor’s Marine Business Development Manager shared his thoughts with me about diesel fuel filters. Primary filters are located between the tank and the engine and secondary filters are typically mounted on the engine. When going this route, Mark suggested using a 30-micron filter as the primary and a 10-micron filter for the secondary element. If you only have one filter on board, it’s best to go with the 2-micron element that will catch just about everything. Racor is one of the few manufacturers that offers three micron ratings for most of their replaceable filter elements. Regarding when to change what, Mark inferred that this was driven more by existing engine vacuum pressures than specific time intervals. For diesel engines, 0 to 10 PSI is the happy zone. At 12 to 13 PSI a yellow caution flag goes up and at 15 PSI it is time for a filter change due to fuel flow restrictions.

Racor makes a number of commercial diesel fuel filter lines, the two most popular are the Spin-On series and the Turbine series. The Spin-On is a simple way to take care of your primary filtration needs. Offered in a variety of flow rates up to 120 gph, the heart of the filter is the canister’s proprietary Aquabloc II medium, which effectively removes water and traps contaminants in its internal baffles. Some of these fuel filters are also offered with handy onboard primer pumps, and all provide an electronic water sensor option. The Turbine series filters are a step up the evolutionary ladder with clear bowls to visualize water and a spinning internal turbine that works to separate water and contaminants from the fuel. Racor also offers some really cool dual and triple filter systems with built-in valves, plumbing and vacuum gauges if you have the need. Mark’s parting advice for boaters was to practice the proven Noah’s Ark principle of marine management…take two of everything, especially fuel filters.