How often should I change my outboard fuel filter?

Outboard fuel filter: how often to change the water-separating filter · Symptom: Your motor stumbles, bogs, or loses power, the see-through filter on the engine shows water or a floating red ring, or you just can't remember when the fuel filter was last changed.

Quick answer: Change the water-separating fuel filter between the tank and the motor at least once a year or every 100 hours, whichever comes first, and right away after a bad tank of gas. Yamaha says to replace its 10-micron fuel/water separating filter every 50 hours, and its see-through on-engine filter every 100 hours. Mercury's Quicksilver guidance is annually or every 100 hours. If you see water in the on-engine filter, change the water-separating filter and check your tank for water.

Likely causes (most to least common)

Filter is overdue and partly clogged, starving the motor at higher throttle
Water in the fuel (condensation, ethanol phase separation, or a bad fuel dock) filling the filter's water trap
Debris from an old tank or a bad tank of gas
Filter loose or its gasket damaged, letting air in so the motor runs lean or the primer bulb won't stay firm
Wrong filter (not rated for your motor's fuel flow, or not 10-micron for a fuel-injected engine)

Safe owner checks & fixes

Work with the engine off and cool, away from sparks or flames, with rags and a catch pan ready. Gasoline vapor is explosive.
Find your filters. Many boats have a spin-on water-separating filter in the fuel line between the tank and the motor, and most modern outboards also have a filter on the engine. Your owner's manual shows where.
Look at the see-through on-engine filter. On Yamaha outboards, a floating red ring means water in the trap; don't remove that ring.
To replace a spin-on filter, unscrew it with a filter wrench and drain it into an approved container. Don't just dump it and reinstall it; Yamaha warns that trapped water and debris can get into the clean side.
Put a thin film of clean engine oil on the new filter's gasket. Yamaha and Quicksilver both suggest this so it seals and comes off easily next time. Hand-tighten per the filter's instructions.
Optionally fill the new filter about three-quarters full with fresh, stabilized fuel (Yamaha's tip) so priming is quicker, then squeeze the primer bulb until firm and check for leaks before starting.
Write the date and engine hours on the filter so you know when it's due. Change it as part of winterizing or your spring start-up.

Parts / tools

Correct replacement water-separating filter for your motor, filter wrench, catch pan, rags, approved fuel container, a little clean engine oil, owner's manual.

Call a marine mechanic when

Water keeps showing up in the filter after you change it; the motor still bogs or stalls with a fresh filter; you smell fuel or see a leak you can't fix by re-seating the filter; or the filter you need to change is inside a fuel-injected engine (Yamaha says its vapor separator tank filter is dealer work).

Sources

Values not stated here are model-specific; check your owner's manual.