Comprehensive Guide: How to Winterize Your Mercruiser Engine

As the leaves turn and the temperatures drop, it’s time to think about preparing your boat for the winter months. If you own a boat with a Mercruiser engine, proper winterization is absolutely crucial to prevent costly damage from freezing temperatures. Neglecting this vital step can result in cracked engine blocks, manifolds, and other components, leading to significant repair bills and a delayed start to your next boating season. This detailed guide will walk you through the necessary steps to winterize your Mercruiser engine effectively, ensuring it’s ready for action when spring arrives.

Why Winterize Your Mercruiser Engine?

Before diving into the ‘how,’ let’s understand the ‘why.’ Water expands when it freezes, and this expansion can exert tremendous force. If water is left in your engine’s cooling system over the winter, it can freeze and crack the engine block, cylinder heads, exhaust manifolds, and other critical parts. This is often irreparable, and the cost of replacing these components can be exorbitant. Winterizing your Mercruiser engine is not just about protecting your investment; it’s about ensuring a smooth and worry-free boating season next year. Additionally, winterizing helps prevent corrosion and helps maintain the overall health of the engine.

Tools and Materials You’ll Need

Before you begin, gather all the necessary tools and materials. Having everything on hand will make the process smoother and more efficient. Here’s a comprehensive list:

• Marine Antifreeze (Non-Toxic, Propylene Glycol): Do NOT use automotive antifreeze. It’s toxic to aquatic life. Propylene glycol antifreeze is the only suitable option. Make sure it’s rated for your local climate. You’ll need several gallons depending on your engine size. Usually 4 to 6 gallons for most engines.
• Engine Flush or Stabilizer: To clean the cooling system. You may choose to use a salt-away type product or a dedicated engine flush. If you are not using a flush, a fuel stabilizer is required.
• Fuel Stabilizer: To prevent fuel breakdown and keep your fuel system healthy.
• Fogging Oil: To protect the engine’s internal parts from rust and corrosion.
• Gear Lube: For your outdrive or sterndrive.
• Outdrive Lube Pump: To refill the outdrive with gear lube.
• Drain Plugs and Washers (if needed): Check their condition.
• Small Bucket or Container: To collect drained fluids.
• Hose and Water Source: For flushing the engine.
• Garden Hose Fittings: A female quick disconnect is helpful for connecting to the engine flush connection.
• Screwdrivers (Flathead and Phillips): Different sizes.
• Wrenches or Socket Set: Metric and/or SAE, depending on your engine model.
• Pliers: For removing hoses and clamps.
• Oil Absorbent Pads or Rags: For cleaning up spills.
• Owner’s Manual: For specific engine details and procedures.
• Optional: A plastic bag and zip ties to seal off the exhaust.
• Optional: A small funnel for pouring fluids.
• Optional: Latex or Nitrile gloves to keep your hands clean.

Step-by-Step Guide to Winterizing Your Mercruiser Engine

Now, let’s get into the actual winterization process. Follow these steps carefully, and always refer to your owner’s manual for specific instructions related to your engine model. It is also important to consult with a qualified marine mechanic if you are unsure about any of the procedures.

Step 1: Prepare the Boat and Engine

1. Safety First: Make sure the boat is on a trailer or stored in a location where it’s secure and stable. Disconnect the battery to prevent accidental starts and to protect electrical components from damage over the winter.
2. Warm Up the Engine: Run the engine for 10-15 minutes to warm up the oil and circulate it throughout the system. This will make the oil change process more effective. Make sure you run the boat with a supply of fresh water going to the engine.
3. Gather your supplies: Now is a good time to stage all your supplies where you can easily access them.
4. Prepare for Oil Change (Optional): If it’s time for an oil change, now’s the time to do it, before flushing and winterizing. Refer to your owners manual for specific oil and filter recommendations.

Step 2: Flush the Cooling System

This is an extremely important step that helps remove debris and minerals from the cooling system. For this step you will need access to a water supply to connect a hose to. You will also need your engine flush or salt-away type product if you choose to use it.

1. Connect the Water Supply: Locate the flush connection on your engine and connect a water hose to it. If you are flushing with Salt-away, be sure you have the appropriate mixing device.
2. Start the Engine: Start the engine and let it run at idle speed. Make sure water is flowing.
3. Run the Flush: If you are using an engine flush or salt away, follow the manufactures instructions for adding this to the water supply. Let this run in the engine for 5-10 minutes.
4. Flush with Fresh Water: If you used an engine flush, now it’s time to flush with fresh water for an additional 5-10 minutes.
5. Turn Off the Engine: Once the flush is complete, turn off the engine and remove the water supply hose.

Step 3: Drain the Cooling System

This step is absolutely critical to prevent freezing damage. Carefully locate all the drain points on your engine. These are usually blue plastic drain plugs or petcocks. Consult your owner’s manual for specific locations. Keep your bucket ready to collect the drained water and coolant.

1. Locate Drain Plugs: On most Mercruiser engines, you’ll find drain plugs on the engine block, exhaust manifolds, and raw water pump. Some models may have more than one drain plug on the manifolds. Consult your engine’s diagram.
2. Remove Drain Plugs: Carefully remove the drain plugs. Be prepared for water to rush out, so make sure your bucket is positioned correctly. Don’t use a tool if the plug is plastic; hand tighten and loosen these only. Inspect the plugs and washers and replace if needed. If you removed plugs from the manifolds, be sure to check all sides of the manifolds for plugs.
3. Drain Thoroughly: Allow all water to drain completely. This may take some time. Ensure the engine is tilted down to allow maximum drainage. Once the initial rush of water has subsided, take a paper towel and poke into the drain holes to clear any debris that might be blocking the drain.
4. Reinstall Drain Plugs (Hand Tight): Once all the water has drained, reinstall the drain plugs. DO NOT overtighten them; they should be snug, hand-tight. Remember to use new washers if needed. DO NOT tighten these with a wrench as over-tightening can lead to cracking.

Step 4: Introduce Antifreeze

Now it’s time to circulate the non-toxic marine antifreeze through the cooling system. This will displace any remaining water and protect against freezing.

1. Prepare the Antifreeze: Have your marine antifreeze ready in a container that you can easily connect to the water intake hose. You may use a bucket, a purpose made container, or even a small garbage can.
2. Connect Water Hose: Connect the hose to the engine flushing port. Connect the other end to the container with the antifreeze.
3. Run the Engine: Start the engine and let it run at idle speed. Observe the exhaust to ensure the engine is drawing the antifreeze through. You will see a color change in the exhaust water (if it was clear water before). Continue running until you see the colored antifreeze coming from the exhaust.
4. Monitor Antifreeze Levels: Keep a close eye on the antifreeze levels, ensuring that the engine is constantly drawing liquid. You may need to add more antifreeze as it is consumed.
5. Run for Several Minutes: Allow the antifreeze to circulate for at least 2 to 3 minutes to ensure all parts of the cooling system are protected. If you are in a very cold region, you will want to run the antifreeze through until it has completely displaced the water coming from the engine and is coming out full strength and color.
6. Shut Down the Engine: Turn off the engine. Disconnect the water hose and the container.

Step 5: Fog the Engine

Fogging the engine is vital for protecting internal components from rust and corrosion during storage. This involves spraying a special fogging oil into the engine’s intake while it’s running.

1. Locate Intake: Locate the air intake on your engine. This may be the carburetor or a connection on the intake manifold.
2. Prepare Fogging Oil: Shake the can of fogging oil well.
3. Start the Engine: Briefly start the engine and keep it running at a low idle.
4. Spray Fogging Oil: Spray the fogging oil into the carburetor or intake. You may need to use your hand to control the spray so the engine does not stop running. The engine will begin to sputter, this is normal. If the engine is fuel injected, you will need to spray this directly into the throttle body.
5. Continue Spraying: Continue spraying until the engine begins to choke and then shuts down. This ensures that a good coating of oil is spread through the engine.
6. Optional: After the engine has shut down, you may want to spray a bit more fogging oil into the intake.

Step 6: Fuel System Stabilization

Fuel can degrade over time, especially during long periods of storage. Fuel stabilizer helps prevent this and protects your fuel system.

1. Add Stabilizer: Add the recommended amount of fuel stabilizer to the fuel tank. Refer to the product label for specific instructions.
2. Run the Engine Briefly (Optional): If you have not already run the engine since the fuel stabilizer was added, run the engine for a few minutes to ensure that the treated fuel circulates through the fuel system.

Step 7: Outdrive/Sterndrive Service

Your outdrive or sterndrive requires special attention during winterization. It’s crucial to drain and replace the gear lube.

1. Locate Drain and Fill Plugs: Locate the drain and fill plugs on the lower unit of your outdrive. They are typically located at the very bottom (drain) and on the side (fill). Consult your owner’s manual for the exact locations.
2. Place Catch Container: Position your bucket under the lower drain plug.
3. Remove Plugs: Remove the drain and fill plugs, being sure to replace the washers. Allow the old gear lube to drain completely. Dispose of the old lube properly.
4. Pump in New Lube: Using your gear lube pump, start pumping new gear lube into the fill hole. Continue pumping until the new gear lube comes out of the drain hole.
5. Reinstall Plugs: Quickly install both the fill and drain plugs, making sure they are securely tightened and do not leak. Replace the washers as needed.
6. Check Lube Level (Optional): After a few days, re-check the gear lube level to ensure there are no leaks.

Step 8: Final Checks and Preparations

With the main winterization steps completed, it’s time to take care of some final details.

1. Battery Storage: Remove the battery from the boat and store it in a cool, dry place. Use a battery tender to maintain charge over the winter if needed.
2. Lubricate Control Cables: Lubricate all the throttle and shift cables with a marine grade lubricant. This will help prevent corrosion and binding of the cables.
3. Seal the Exhaust (Optional): To prevent insects and rodents from entering the engine, seal off the exhaust outlets with plastic bags secured with zip ties or tape.
4. Boat Cover: Cover your boat with a well-fitting boat cover to protect it from the elements.
5. Check Bilge: Make sure the bilge is clean and dry.

Important Considerations

• Consult Your Owner’s Manual: Always refer to your specific Mercruiser engine’s owner’s manual for detailed instructions and recommendations.
• Professional Assistance: If you’re uncomfortable performing any of these steps, consult a qualified marine mechanic.
• Climate Conditions: Adjust your winterization procedures based on the climate conditions in your area. Extremely cold climates may require additional precautions.
• Record Your Work: Keep a record of when you winterized your boat and what steps you took. This can be helpful for next year.

Conclusion

Winterizing your Mercruiser engine may seem like a lot of work, but it’s a necessary investment that will prevent costly repairs and ensure your boat is ready to go when the boating season begins. By following these detailed steps carefully and being mindful of the specifics of your engine model, you can confidently prepare your boat for a safe and worry-free winter. Remember that consistency and thoroughness are key to protecting your investment. Happy Boating!