Winterizing Outboard Boat Engines: A Step-By-Step Guide

Winterizing an outboard boat engine is essential to protect it from damage during the colder months. When a motor isn't properly winterized, water can freeze and expand, causing cracks and breaks. Winterizing your boat engine will save you time and energy when the warmer season arrives, and it will also help to maximize the lifespan of your boat. The process of winterizing an outboard boat engine includes several simple tasks, such as flushing the engine with fresh water, changing the oil and oil filter, spraying the engine with fogging oil, and storing the engine in a dry place.

Flush the engine with fresh water

Flushing your outboard boat engine with fresh water is an essential part of boat maintenance. Salt build-ups inside your motor can cause costly issues down the line, so it's important to flush your motor after every use.

There are two recognised methods for flushing your outboard engine with fresh water: using flushing muffs or a flushing port.

Using Flushing Muffs

• Put the muffs around the front of the gearbox, away from the propeller, ensuring that the water intake grills on the side of the gearbox are fully covered.
• Attach a hose to the muffs and turn it on.
• Start the engine and leave it running in neutral.
• Do not leave the engine unattended.
• Do not run the engine in gear.
• Run on muffs for no more than 15 minutes.
• When finished, turn off the engine and then the hose and remove everything.
• Leave the engine in the down position to drain out all the remaining water.

Using a Flushing Port

• Identify the flushing port cap and remove it.
• Attach the flushing attachment.
• Fit your hose to the flushing attachment and turn on the water.
• Do not start the engine.
• Run the water for at least five minutes.
• When complete, remove the flushing attachment and replace the flushing port cap.
• Leave the engine in the down position to drain.

General Tips

• It is important to run the motors long enough for the thermostat to open, allowing the fresh water to flush the salt from the entire powerhead.
• Make sure you have good water flow when flushing your engine.
• Do not walk away from your motor while it's running.
• It is recommended to flush your engine after every use, and every six weeks if it has been sitting in storage.

Change the engine oil and oil filter

Changing the engine oil and oil filter is an important part of winterizing your outboard boat engine. It is recommended that you change the engine oil and oil filter every 100 hours or once a season, regardless of how many hours the engine was used. This is because storing the motor with old oil can expose internal engine components to moisture and acidic combustion byproducts, which can cause corrosion.

• Warm up the engine: Before changing the oil, it is recommended to warm up the engine to ensure that the crankcase oil gets warm and flows easily for more complete draining.
• Access the drain screw and oil filter: Depending on the make and model of your engine, you may need to remove the lower cowls or cowlings to access the drain screw and oil filter.
• Place a drain pan: Before removing the drain screw, place a drain pan underneath to catch the oil. You may also want to lay a barrier on the ground to protect against spillage.
• Remove the drain screw: Once the pan is in place, remove the drain screw. Some engines have a drain plug, while others have a drain screw.
• Remove the old oil filter: Take out the old oil filter. You may need an oil filter wrench if it was tightened too much.
• Lubricate the O-ring seal: Before installing the new oil filter, lubricate the O-ring seal at the top with fresh oil.
• Install the new oil filter: Hand-tighten the new oil filter until the gasket makes full contact. Then, tighten it further by about 3/4 of a turn.
• Refill the crankcase with fresh oil: Refill the crankcase with the manufacturer's recommended amount and type of marine four-stroke outboard oil.
• Check the oil level: After adding the new oil, check the oil level with the dipstick and top up if necessary.
• Start the engine: Start the engine and let it idle for 15 to 30 seconds. This will distribute the new oil throughout the crankcase and cylinder head and fill the filter.
• Stop the engine and check the oil level again: After idling the engine, stop it and check the oil level again. Add extra oil if it is below the maximum level.
• Grease all fittings: Use a grease gun with a Zerk fitting to grease all fittings on the outboard with marine waterproof grease.

It is important to note that marine oils are specially formulated for harsh and wet conditions, prolonged periods of inactivity, and higher exposure to potential rust and corrosion. Therefore, always use marine four-stroke oil and never use automotive oil in a marine engine. Additionally, properly dispose of the waste oil and filter to avoid environmental damage.

Prepare the fuel system

Preparing the fuel system is a crucial step in winterizing an outboard boat engine. Fuel, when left untreated, can begin to oxidize and form a gum-like substance in the engine's fuel system. This is especially true for outboards equipped with carburetors. To prevent this, it is recommended to always store your boat with fresh fuel that has been treated with a marine fuel stabilizer.

First, if possible, try to run your boat's fuel tank almost empty at the end of the season. Then, add fresh fuel before storage. If the fuel in the tank is more than a month old, it is best to have it pumped out and replaced with fresh fuel. This is an important step as fuel stabilizer works best when added to fresh fuel.

Next, fill your gas tank to 95% capacity. It is important not to fill it completely as extreme temperature changes can cause the fuel to expand, potentially forcing gas out of the vent. Once the tank is filled, add the correct amount of fuel stabilizer to the fresh fuel. Treating the fuel with a stabilizer will prevent it from oxidizing and leaving behind varnish-like deposits.

Now, you'll want to get that treated fuel into the entire fuel system. To do this, run the boat for about 10 minutes, either in the water or while connected to a garden hose. Be sure to follow the instructions in your owner's manual for this step.

Finally, replace the fuel filter, and your motor's fuel system will be ready for the next boating season.

It is important to note that these steps are general guidelines, and specific engines may have unique requirements. Always refer to your owner's manual or service manual for engine-specific winterizing instructions.

Fog the engine with lubricant

Fogging your boat engine is an essential part of the winterizing process. It is an inexpensive and simple way to protect and extend your engine's life. Fogging oil is a waxy oil that you spray into your engine to coat its components and protect them from corrosion while in storage. It is an aerosol petroleum treatment that provides long-term lubrication and corrosion resistance. When properly administered, it forms a thin film on metal components that, unlike oil, remains intact over time.

• Start the engine and remove the air filter.
• While the engine is running, spray fogging oil into the air intake of each cylinder.
• After 10 seconds, shut off the engine.
• Remove the spark plugs carefully.
• Spray fogging oil into each cylinder via the included extension tube for three seconds.
• Replace the spark plugs.

Note that fogging oil should not be used on diesel engines. It is also important to consult the manual and collect the necessary tools and products before beginning the process. Additionally, ensure that the engine is warm before treating it with fogging oil.

Store the engine upright

When storing your outboard boat engine, it is important to keep it upright. This is because, if water gets into the engine and freezes, it can cause serious damage. By storing the engine upright, you allow any remaining water to drain out.

If you are storing your boat on a trailer or a rack, you should trim the motor down to its vertical position. This will ensure that any water left in the engine can self-drain. If water is trapped inside the engine and the temperature drops below zero, the water will freeze, expand, and put immense pressure on the engine's components, which may break under the strain.

Additionally, it is worth noting that mice can sometimes be a problem. They may be able to get under the motor cowl and chew on the wiring. Some people recommend placing fabric softener sheets, or dryer sheets, around the engine as these are believed to repel mice. Just remember to remove the sheets before taking your boat out on the water again.

By storing your outboard engine upright and taking the necessary precautions, you can help ensure that your engine stays in good condition during the off-season and is ready to go when the boating season starts again.

Frequently asked questions