Protect Your Boat's Fuel System From WaterWater in an engine’s fuel system is never good. “It doesn’t take much corrosion to make a diesel fuel injector stick,” says John Strauss, West Palm Beach, FL. With either gas or diesel, water in fuel can kill expensive components without warning. Fortunately, quick action at the first sign of water in your boat’s fuel system can help you avoid repair bills altogether. Check out these five tips.

1. Water sits under the fuel in a distinct layer. “If you’re offshore and the bowl is less than a quarter full of water, drain the water and change the filter,” Strauss says, and then head in cautiously. Gas inboards require metal filter bowls. Drain water from the valve in the bottom, and be sure to reinstall the safety plug in the drain valve.

2. Primary filters (the first filter after the fuel tank) block small amounts of water, but a large gulp might make it through. To check, dump fuel from the secondary filter (a spin-on canister attached to a diesel or an in-line filter on most gas engines) into a bucket and look for water globules.

3. Flush clean fuel from a jug through the engine to the connection at the high-pressure diesel injection pump or the gasoline injector supply rail using a filtered line. Most diesels have a manual fuel pump near the secondary filter or on the low-pressure supply pump. On gas engines, “turn the ignition on and off. That runs the electric fuel pump for 10 seconds or so,” Strauss says.

4. “If the motor stalled because of water, loosen diesel injector lines and turn it over with the starter until you get clean fuel there too,” Strauss says. For gas engines, “remove a sensor or plug at the far end of the supply rail and flush it there.” Drain water from a lift-type muffler or close the raw-water intake if cranking an engine for more than 30 seconds or so.

5. Clean the tank and find the cause. Deteriorated fuel fill-cap O-rings or gauge sender gaskets are common entry points. Be sure that tank vent lines run upward before turning down toward the tank, and pressure-test return fuel coolers.

Quick Tip: Shine a light through fuel-filter inspection bowls. Fuel should be “clear and bright” golden or red. Drain water or sludge from the valve in the bottom.

Diesel Filter Color Code
Racor uses color coding so choosing the right filter is easier. Red 30-micron filters pass extra fuel to cool fuel-system components. New common-rail diesels might use blue 10-micron filters. On generators, use brown 2-micron elements in oversize Racor filter assemblies.

Source:; Capt. Vince Daniello; July 14, 2014.