Most outboards have two levels of fuel filtering: a small filter on the engine and, ideally, a larger water-separating fuel filter mounted in the boat between the tank and the engine. The water separator catches water and debris before they reach the engine, which matters with ethanol fuel. A clogged or water-filled filter causes hard starting, loss of power at higher speeds, surging and stalling.
Outboard fuel filter symptoms
- Engine runs at idle but loses power or stutters at full throttle; see outboard loses power at full throttle
- Stalls after running for a while
- Hard starting or long cranking
- Water or debris visible in a clear filter bowl
- Primer bulb going soft while running; see outboard primer bulb
Outboard fuel filter and water separator
A water-separating filter uses a spin-on element that lets water settle and traps fine particles. Many boaters fit one if the boat does not already have it, especially when running ethanol fuel; see ethanol in boat fuel. Mount it where you can reach it, with the arrow pointing toward the engine.
Replacing an outboard fuel filter
- Close the fuel supply or disconnect the line and have rags ready.
- Remove the old filter or element and check the fuel in it for water.
- Fit the new filter with its seals lubricated with clean fuel or oil as directed, and tighten as specified.
- Prime the system with the primer bulb and check for leaks before starting.
Many owners replace water-separating filters every season and the engine-mounted filter at the interval in the manual.
How often to change it
Change the water-separating filter at least once a season and whenever it collects water. Boats that use ethanol fuel, sit for long periods or run in humid climates may need it more often. Engine-mounted filters often have their own interval in hours.
Draining the separator
Some water-separating filters have a drain at the bottom or a clear bowl. If you see water, drain it into a container until clean fuel appears, then find out how the water got in: bad fuel, condensation or a leaking deck fill.
Fuel filter not staying full
On engines with a clear filter bowl, a bowl that does not stay full of fuel while running usually means air is getting in through a loose fitting, a cracked line or a bad primer bulb, or the engine is struggling to draw fuel past a restriction such as a closed tank vent or a sticking anti-siphon valve.
Related problems
If the filter is clean and the motor still runs badly, see outboard won’t idle, outboard runs rough and outboard won’t start. For routine care see outboard motor maintenance.
More guides: outboard fuel lines.
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