Changing Fuel Filter: Mercruiser 350 Mag Maintenance Guide

Changing the fuel filter on a Mercruiser 350 Mag engine is a straightforward task for boat owners. It is recommended that the fuel filter be changed annually or after every 100 hours of operation. This is because any water trapped in the filter could corrode the filter canister. The procedure for changing the fuel filter is outlined in the Mercruiser 350 Mag engine owner's manual, which can be downloaded or ordered from MercuryMarine.com or an authorised dealer.

Safety precautions

Changing the fuel filter on a Mercruiser 350 Mag engine requires several safety precautions to be taken to ensure your safety and avoid damage to the engine. Here are the key safety precautions to follow:

Firstly, fuel is highly flammable and explosive, so it is crucial to ensure that the key switch is turned off and the lanyard is positioned to prevent the engine from accidentally starting. Do not smoke or allow any sources of sparks or open flames near the work area. Keep the area well-ventilated to avoid prolonged exposure to vapors.

Before starting any work, allow the engine to cool down. Mercury MerCruiser recommends shutting off the engine for 12 hours before attempting to remove the filter. This will reduce the risk of fire and allow the engine to be handled safely.

When working on the fuel system, always wrap the water-separating fuel filter with a cloth. This will help catch any fuel spills or spray and minimize the risk of fuel coming into contact with hot engine components. It is also important to clean up any spilled fuel immediately to prevent fires and potential damage to the engine.

Before reconnecting the Cool Fuel Module harness to the engine wiring harness, ensure the fuel supply valve is closed if your engine is equipped with one. This will prevent any fuel leaks during the disconnection and reconnection process.

After completing the fuel filter replacement, always check for leaks before attempting to restart the engine. If any leaks are detected, stop the engine immediately, and do not attempt to restart it. Recheck the filter installation, clean up any spilled fuel, and ventilate the engine compartment. If leaks persist, do not attempt to fix the problem yourself. Instead, contact your authorized Mercury MerCruiser dealer for assistance.

Engine preparation

Before starting any work on your engine, it is important to take the necessary precautions to ensure your safety and the protection of the engine. Here are the steps you should take to prepare the engine for a fuel filter change on a Mercruiser 350 MAG:

Step 1: Allow the Engine to Cool Down

First, make sure the engine is switched off and allow it to cool down completely. Mercury MerCruiser recommends that the engine be shut off for at least 12 hours before you begin the fuel filter replacement process. This is an important safety measure to prevent any risk of fire or explosion.

Step 2: Ensure Proper Ventilation

Fuel is highly flammable and explosive, so it is crucial to work in a well-ventilated area. Make sure the work area is open and airy to prevent the buildup of flammable vapors. Keep the engine compartment properly ventilated throughout the entire process.

Step 3: Position the Lanyard

Position the lanyard correctly to ensure that the engine cannot start accidentally during the service. This is a safety measure to prevent any unexpected engine startups that could cause injuries or accidents.

Step 4: No Smoking or Open Flames

Do not smoke or allow any sources of sparks or open flames in the vicinity of the engine while you are working on it. This is a critical safety precaution to prevent any potential ignition of fuel vapors or spills.

Step 5: Close the Fuel Supply Valve

If your engine is equipped with a fuel supply valve, make sure it is closed before proceeding. This will prevent any fuel leaks or spills during the filter replacement process.

Step 6: Prepare the Necessary Tools and Materials

Gather all the necessary tools and materials, such as an adjustable filter wrench, rags or paper towels, a catch pan, and a container for the drained fuel. Having everything you need at hand will make the process smoother and help you avoid any last-minute hassles.

Step 7: Wrap the Fuel Filter

Wrap the water-separating fuel filter with a cloth or rag. This will help catch any fuel spills or spray that may occur when you remove the filter. It is a precautionary measure to minimize the risk of fuel leakage during the replacement process.

Now that you have completed the engine preparation steps, you can proceed to safely replace the fuel filter on your Mercruiser 350 MAG, following the manufacturer's instructions and safety guidelines.

Disconnecting the fuel supply

To disconnect the fuel supply of your Mercruiser 350 MAG MPI, follow these steps:

Firstly, ensure the engine is off and that the lanyard is positioned so that the engine cannot start. This is crucial as fuel is highly flammable and explosive. Do not smoke or allow any sources of sparks or open flames in the area while servicing. Keep the area well-ventilated and avoid prolonged exposure to vapors.

Next, allow the engine to cool down. It is recommended by the manufacturer that the engine be shut off for 12 hours before you proceed with any further steps.

Once the engine is cool, locate and close the fuel supply valve, if your engine is equipped with one. This will prevent any further fuel flow and reduce the risk of spills or leaks during the filter change.

Now, wrap the water-separating fuel filter with a cloth. This is an important step to catch any fuel that may spill or spray during the disconnection process.

At this point, you can proceed to remove and discard the water-separating fuel filter and its sealing ring from the mounting. Be cautious and ensure that you have a catch pan or container ready to collect any spilled fuel.

Finally, coat the sealing ring on the new filter with engine oil before proceeding with the installation process.

Removing the old filter

To remove the old filter from your Mercruiser 350 Mag engine, you will need to follow the steps outlined in the engine's owner's manual. Here is a detailed guide on how to do it:

Firstly, ensure that you have allowed the engine to cool down. Mercury MerCruiser recommends that the engine be shut off for 12 hours before you begin any maintenance work. This is an important safety precaution as fuel is flammable and explosive. Make sure the key switch is off and the lanyard is positioned so that the engine cannot start accidentally. It is also recommended to work in a well-ventilated area and avoid any sources of sparks or open flames.

Once the engine has cooled down and all safety precautions have been taken, locate the fuel supply valve and close it if your engine is equipped with one. This will prevent any further fuel flow to the filter.

Now, you can proceed to remove the old filter. Place a cloth around the water-separating fuel filter to catch any fuel spills or spray that may occur during the removal process. This will help contain any potential messes and minimise the risk of fuel getting on your skin or other components. Carefully remove the old filter and the sealing ring from the mounting. Be cautious as the filter may still contain some fuel.

Dispose of the old filter and sealing ring properly. It is important to handle and dispose of the old filter responsibly to prevent any environmental hazards. Check with your local waste management guidelines or consult a professional if you are unsure about the proper disposal methods for fuel filters.

By following these steps, you will be able to safely and effectively remove the old fuel filter from your Mercruiser 350 Mag engine. Remember to refer to your engine's owner's manual for specific instructions related to your particular engine model.

Installing the new filter

To install the new filter, first lubricate the rubber gasket with a small amount of engine oil, applied with a rag or your fingertip. This will prevent the gasket from being displaced or damaged when the filter is tightened on the engine. Next, coat the sealing ring on the new filter with engine oil.

Then, select the appropriate size connector for the fuel line and install the connector on the new filter. Apply sealant to the male pipe threads on the connectors. Torque each connector using a backup wrench on the hex fitting nearest to the connector. Insert the filter into the mounting clip and install and torque the screw and washer through the mounting clip into the stringer.

Finally, reconnect the Cool Fuel Module harness to the engine wiring harness.

Frequently asked questions