The fuel filter on a Mercruiser prevents water and particulate matter from contaminating the fuel. For this reason, it's important to replace the removable filter element regularly.
Different Mercruiser engines use different fuel filter elements, so check your owner's manual to find the correct part number. Once you have the replacement filter, finding and changing the old one is a relatively simple procedure with the right tools.
Items you will need
Socket set
Rag
Filter wrench
Replacement filter element
Motor oil
Disconnect the boat's battery cables to prevent the possibility of a spark while you are working with the fuel system. Otherwise, there is a risk of fire.
Place a rag beneath the fuel filter to catch any leaks or drips. The fuel filter, a white cylinder, is located along the fuel line going into the engine.
Use a filter wrench to loosen and remove the filter element. Coat the o-ring on the replacement fuel filter with a small amount of motor oil to prevent sticking. Thread the new fuel filter element onto the adaptor and hand tighten.
Tighten the filter element an additional half-turn with the filter wrench. Don't over-tighten it, or it will be very difficult to remove later.
Remove the rag from beneath the fuel filter. Reconnect the battery cables and start the engine. Check around the fuel filter for leaks, and tighten it if necessary.