How to Change a MerCruiser's Water Separating Fuel Filter

A MerCruiser is an inboard motor for a boat. Boat motors require routine maintenance to keep them running smoothly year after year. Changing a water separating fuel filter is part of that routine. The water separating fuel filter's primary function is to keep water out of the gas line. Here is how to change the water separating fuel filter on a MerCruiser.

Read your MerCruiser motor owner's manual. The owner's manual is the best place to begin with any maintenance or repair.

Purchase a new fuel filter at a marine parts store. You'll need your model number and serial number in order to buy the right filter for your motor.

Disconnect and remove all batteries from your boat. Never work with any kind of fuel or fuel parts with a connected battery.

Place a pan under the fuel filter to catch any spillage.

Remove the old fuel filter with a fuel filter wrench and pour any remaining fuel into the pan.

Inspect the filter brackets and make sure nothing is broken or needs replacing. Dry the filter brackets and filter area thoroughly before putting the new filter in place.

Make sure the new fuel filter's O ring is in the proper position and screw the new filter into place.


  • Put a little clean fuel on the fuel filter to make your next start up easier.
  • Don't over tighten the new fuel filter but make sure to screw it into place with the filter wrench.
  • Always work in a well ventilated area when working with any type of fuel system equipment.

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