The Outboard Expert: Do-It-Yourself Filter Installation

Installing a 10-micron water separator/fuel filter is worth the effort.

26th June 2007.
By Charles Plueddeman

Water in contaminated fuel accumulates in the blue reservoir at the bottom of this Suzuki water separator/fuel filter. The fitting on the bottom can be opened to drain water from the filter. This compact-size filter is a good choice for smaller boats.

Water in contaminated fuel accumulates in the blue reservoir at the bottom of this Suzuki water separator/fuel filter. The fitting on the bottom can be opened to drain water from the filter. This compact-size filter is a good choice for smaller boats.

For more than a year I’ve been telling anyone who asks that the best way to avoid fuel-related problems with any outboard is to install a 10-micron water separator/fuel filter on the boat. Suzuki and Yamaha ask their boat-building partners to install a 10-micron filter on new boats rigged with its motors to head off issues related to water-contaminated gasoline and fuel fouled with other compounds, a situation that has become more prevalent in many markets with the introduction of E-10 fuel, a blend that includes up to 10 percent ethanol.

This Crestliner didn't offer room on the transom for installing a fuel filter, so we had to look for a spot below the deck.

This Crestliner didn't offer room on the transom for installing a fuel filter, so we had to look for a spot below the deck.

I think a lot of offshore fishing boats are coming equipped with factory-installed fuel filters, but I’m not seeing them on many inland fishing boats. I was just looking at a new Lund last weekend, for example, that did not have a filter. And of course, there’s a huge fleet of older boats out there with no filter other than the small screen on the motor, including the Crestliner belonging to my buddy Arlyn. And because I might go fishing with Arlyn, I don’t want his motor to conk out from a fuel problem. So I proposed that we use his boat to demonstrate how easy it is to install a good fuel filter.

I honestly thought this would be a 15-minute job, but it turned out the project took two weekends and pushed my frustration meter to yellow. But we probably learned more with this tricky installation than we would have from a easy job. Our subject boat is a 2001 Crestliner 1700 Super Hawk, powered by a 2001 Evinrude 70 four-stroke, which is really a Suzuki DF70 with blue paint and Evinrude decals. Suzuki (www.suzukimarine.com) supported this project by donating a filter kit. Suzuki offers two filters kits, the standard size (P/N 99105-20005-ASY, $71.95, $23.95 for a replacement element) and the compact size (P/N 99105-20006-ASY $60.00, 19.95 for a replacement element).

The kit includes the cast-aluminum filter head and the filter element, plus a blue plastic reservoir that screws on below the element. If there’s water in the fuel, it should end up in the reservoir, where you can see it and also drain it out through a fitting on the bottom. Both of these filters are manufactured by Racor, and Racor filter elements will fit on the heads and are widely available, and you’ll want to buy a spare element right away to keep on board.

The best way to install one of these filters is to mount it right on the inside (boat side) of the transom, if there is room. This makes it easy to see the filter and to check for water, and also makes it easy to change the element, which should be done annually. Unfortunately, the Super Hawk has a very compact splashwell and a low transom, maybe great for fishing but there was no room to hang the filter. There was room in the battery locker to starboard, but that would make a long run for the fuel line, and I didn’t like the idea of putting a vessel of fuel right next to the battery.

We popped off the access port to the bilge, and finally determined that the only place to locate the filter would be on one of the “knee” braces between the transom and hull. However, there was no way that the standard filter, which is about eight inches tall and four inches in diameter, would fit in this space.

We also discovered that Crestliner did not provide access to the fuel line fittings on the top of the tank, which is located below the aft deck. We were going to have to remove the deck to get to the fuel lines.

The Suzuki compact filter is about half the size of the standard filter, and still rated for up to 140 hp (but not for V6 motors). This filter would fit below decks in the Crestliner. We were careful to make sure that we’d have enough room below the filter to drain the separator to check for water, and to change the filter. An electric screwdriver helped speed up the task of removing about 20 screws to loosen the side panel and about three-quarters of the deck. We found we could lift the deck up enough to reach the tank fittings without removing it completely.

Our contact at Suzuki, applications expert David Greenwood, told me there were a number of ways to screw up this installation, so we considered his advice as we worked:

A tight fit, but it works. We located the filter head on a support knee. It can be reached for service through the access port in the splash well.

A tight fit, but it works. We located the filter head on a support knee. It can be reached for service through the access port in the splash well.

Avoid adding any unnecessary restriction to the fuel lines. Don’t use 90-degree fuel fittings. Don’t use fuel line barbs that are too small. Try to add as little extra length to the overall fuel line as possible. Like many late-model outboards, the Suzuki DF70 has an electric lift-pump that draws fuel from the boat tank into a reservoir on the motor, that in turn supplies fuel to the high-pressure fuel injection pump. Too much restriction in the fuel system could make it difficult for the lift pump to keep up with the motor. Greenwood says that if your motor dies after a long run at wide-open throttle, and you have to use the primer bulb to get the motor started, you probably have too much restriction in the line. The filter itself will add some restriction, but the motor is designed to handle that.

Bigger fuel line is not better. To avoid restriction problems, it might seem logical to use larger-diameter fuel line, but this exactly the wrong this to do, according to Greenwood. The pump on the motor is working to lift the weight of all the fuel in the line from the tank. If you go from 5/16-inch line to 3/8-inch line, for example, you’ve increased the volume, and the weight, of the fuel in the system, and you’ll be making that pump work harder. Make sure the boat is rigged with correct-diameter fuel line. We found that Arlyn’s Crestliner with rigged at the factory with 3/8 OMC fuel line. But Suzuki specs 5/16 line for the DF70. In this case it was working OK, but on some boats the larger-size line might create a problem.

Working through the access port made it tricky to drill the two holes required to mount the filter head, but we finally accomplished that task after much fussing and cursing. We used stainless steel bolts with locking nuts to secure the head. You can use either Teflon pipe dope or Teflon tape when threading the bronze fuel line barbs (not included with the kit) to the filter head. When using the tape, make sure that no tape wraps over the inside end of the barb, another common source of fuel-line restriction, according to Greenwood. And take care to get the threads started correctly into the soft aluminum of the filter head.

We ran one fuel line from the tank fitting directly to the inlet side of the filter (marked with an “in” arrow on the head) and the outlet line directly to the fuel barb that passes through the motorwell. We took care to keep the lines as short as possible without bending the line so far as to kink or restrict it. Aluminum shavings from drilling the mounting holes were vacuumed out of the bilge so they would not foul the bilge pump.

A few squeezes and the primer bulb had the filter full, and the motor started right up after we backed down the launch ramp. Some motors can be hard to start after this installation, because they need to “digest” all of the air in the new fuel line and filter. We left the deck loose for this first test so we could double-check all of the fuel fittings with the engine running.

In this installation, you can’t really see the plastic part of the filter where water would accumulate, so Arlyn is going to check for water once a week or so by draining a little gas out of the bottom into a can he can position below the filter. The presence of water might indicate that some condensation is collecting in the boat’s fuel tank, or that he’s getting water-contaminated fuel at his gas station. If checked regularly, this type of filter not only keeps the water out of the motor, it gives an early warning of water contamination.

Editor’s Note: Charles Plueddeman is the editor at large for Boating, the nation’s largest boating magazine.


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Charles Plueddeman

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Charles Plueddeman is Boats.com's outboard, trailer, and PWC expert. He is a former editor at Boating Magazine and contributor to many national publications since 1986.

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