Water in your boat’s fuel system can spoil an otherwise great day of boating. There are several ways water can contaminate your boat fuel, including condensation forming in the fuel tank, an improperly located fuel tank fill or vent, or from a contaminated supply at a fuel dock or filling station. Ethanol-blended fuels are especially sensitive to these problems. Ethanol in gasoline attracts water, and it’s possible for the ethanol to absorb enough moisture that water, which is heavier than gasoline, will drop to the bottom of the fuel tank. This is called phase separation. If this water/ethanol phase reaches the fuel inlet it can be drawn into the engine and cause poor performance or even damage. These problems can be avoided by routinely replacing your engine’s fuel filter.

A water-separating fuel filter is designed to protect your engine from water that does enter the fuel system. Most modern outboards are equipped with a fuel filter mounted on the engine. Some boat models are also rigged with a remote water-separating fuel filter located on the boat between the fuel tank and the engine.

Your fuel filter should be changed annually, or after every 100 hours of operation. For many boat owners, changing the fuel filter is part of an annual service performed before winter or offseason storage, along with an engine oil-and-filter change and fuel treatment.

This series of step-by-step videos demonstrates how to replace the fuel filter in a variety of Mercury outboard models. Although the location of the filter may vary by model, the basic procedure is similar for most Mercury models. In all cases, your Mercury engine operation and maintenance manual will outline the steps for your specific engine. If you don’t have an owner’s manual or service manual, a copy may be downloaded or ordered directly from MercuryMarine.com or from a Mercury Authorized Dealer.

Essential Tools

Changing the fuel filter requires an adjustable filter wrench, rags or paper towels, a catch pan and a container for the fuel drained from the filter. A premium Quicksilver® Water Separating Fuel Filter offers OEM-quality fit and performance and is available for Mercury and many other brand outboard engines.

Pro Tip: Before installing the new fuel filter, lubricate its rubber gasket with a small amount of oil or grease, applied with your fingertip. This will prevent the gasket from being displaced or damaged when the filter is tightened on the engine.

How to Change a Fuel Filter in a Mercury 150hp FourStroke Outboard

How to Change the Fuel Filter on a Mercury 350hp Verado Outboard