How to Winterize Your Outboard Motor: A Complete Guide

As boating season comes to an end and winter months set in, it’s crucial to prepare your boat for storage. Proper winterization prevents freeze damage, corrosion, and costly repairs, ensuring that your outboard motor is ready to go when warmer weather returns. Whether you have an outboard motor, an inboard engine, or a diesel engine, taking the necessary steps to protect your investment is essential.

Why Winterization is Essential

When temperatures drop, any residual water left inside your boat motor can freeze, causing expansion that leads to cracks in the engine block, exhaust manifolds, and other internal components. Using non-toxic antifreeze and draining all water intake systems can prevent severe damage. Fuel degradation is another risk; untreated fuel can lead to phase separation, causing your boat engine to stall or fail when you need it most. Additionally, failing to check the battery charge level or properly store fuel can result in starting problems when the boating season returns.

Essential Tools and Supplies

Before you start, gather the following supplies:

• Fresh engine oil and oil filter

• Fuel stabilizer

• Fogging fluid

• Non-toxic antifreeze

• Drain plugs

• Spark plugs

• Gear lube pump

• Marine grease

• Flush kit

• Trickle charger (if storing for long periods)

• Outboard oil

• Gasoline engine additive

• Corrosion inhibitor

• Boat engine diagnostics

Step-by-Step Winterization Process

Step 1: Change the Engine Oil and Oil Filter

Old engine oil contains contaminants that can damage internal components during storage. To prevent this, drain the engine oil and replace it with fresh oil. Make sure to use an oil filter wrench to remove and replace the filter. Check your engine manual for specifics on oil type and change intervals. For 4-stroke motors, this step is especially important to maintain engine health.

Step 2: Stabilize the Fuel System

Fuel degradation is a major concern during winter storage. Add a high-quality fuel stabilizer to the gas tank and run the engine for a few minutes to circulate the treated fuel through the entire fuel system. This prevents gum and varnish buildup in fuel injectors, fuel lines, and the carburetor. If possible, fill the fuel tank to reduce condensation, which can lead to water contamination. Many boat owners opt for a fuel injector cleaner at this stage to ensure smooth performance when restarting the engine.

Step 3: Flush the Cooling System

Using a garden hose fitting, connect a flush kit to the motor and run clean water through the cooling system. This will remove any salt, dirt, or debris that could cause blockages. If you have fresh-water cooled engines, ensure that the cooling passages are completely flushed before adding non-toxic antifreeze. It’s also a good idea to inspect the water intake system and drain hole for any obstructions.

Step 4: Fog the Engine to Prevent Corrosion

Fogging the engine is essential to protect internal engine components from rust and corrosion. Spray fogging fluid into the air intakes while the motor is running, ensuring a light coat covers all internal parts. For outboard engines with fuel injectors, follow the engine manual for fogging procedure details. This step is critical for both EFI motors and DFI two-stroke engines.

Step 5: Drain and Refill the Gearcase

Water can accumulate in the gear lube, leading to freeze damage. To prevent this, drain the old gear lube and replace it with fresh unit oil. Check for contaminants in suspension—if you see milky or foamy oil, water intrusion could be an issue, and you may need to inspect the prop shaft seals. Also, check the stuffing boxes and grease fittings for wear and apply marine grease where necessary.

Step 6: Inspect and Replace Spark Plugs

Old or worn-out spark plugs can cause engine stalls and misfires when you restart the motor in the spring. Remove the spark plug holes, inspect them, and replace them if necessary. Apply a small amount of marine grease to the threads to prevent corrosion. It’s also a good idea to check the tilt tube for any excessive wear and lubricate it.

Step 7: Lubricate and Grease Fittings

Apply marine grease to the prop shaft, tilt tube, and other grease fittings. This prevents corrosion and ensures smooth operation when you start the motor after storage. Don’t forget to check the power trim fluid and replenish it if needed. If you have an outboard drive, ensure that all moving parts are properly lubricated.

Step 8: Remove and Store the Battery

If your boat has an electric outboard motor or lithium-ion batteries, disconnect them and store them in a dry, cool place. Use a trickle charger to maintain the battery charge level over the winter. Battery failure due to improper storage is a common issue, so checking terminals and ensuring they are clean will help extend battery life.

Step 9: Cover and Store the Boat Properly

Protect your boat from the elements by using a weatherproof cover. If possible, store the boat in an indoor facility or shrink-wrap it for added protection. Drain any remaining water from bilge pumps, livewell pumps, and other systems to prevent freezing. Additionally, using a corrosion inhibitor on the metal components will prevent rusting over the winter storage period.

Common Boat Motor Winterization Services and Their Benefits

Final Check: Review Your Boat Owner’s Manual

Before finalizing winterization, review your service manual to ensure you’ve covered all necessary steps. If you’re unsure about any procedures, consider hiring a service professional for proper winterization. Some boat owners choose to winterize at an authorized boat repair service to ensure everything is done correctly.

Conclusion

Winterizing your outboard motor might take some time, but it’s well worth the effort. Proper winter storage prevents costly repairs, extends the lifespan of your boat motor, and ensures a hassle-free start to the next boating season. By following this checklist, you’ll be ready to hit the water as soon as the weather warms up! Don’t forget to perform a final inspection in the spring to ensure all systems are in working order before launching back into the water.