How to Winterize an Outboard Motor - A Step-by-Step Guide

Recommendation: Fill the fuel tank with gasoline treated with a high-quality stabilizer, then run the engine until the stabilizer circulates through the lines. The following actions bring condensation and gum buildup under control, making it easy to store the craft and save money in spring.

Next, apply fogging oil into each cylinder port or intake to guard against condensation and corrosion during inactivity. Carefully wipe a thin coat of grease on the propeller shaft and seals, then install protective covers on openings to keep dust away and moisture out. This common practice helps provide readiness for startup.

Flush the cooling passages with clean water until clear, then apply a corrosion-preventive treatment designed for marine engines. This reduces the risk of rust and deposit buildup that can cause trouble later in operation, and it helps you avoid costly breakdown when you reintroduce the craft to operation.

With the fuel system addressed, remove ethanol-containing products if possible and store fuel in a sealed container; if that isn’t feasible, use an inline stabilizer and drain the carburetor or injectors as needed. This precaution reduces varnish and gum, and it can save money and time during reactivation. For additional protection, inspect fuel lines and clamps and replace worn components as needed. If you need extra assurance, this step also includes a fuel treatment that controls moisture and prevents varnish from forming in lines until spring.

Keep the battery charged or remove and store in a cool, dry place; maintain a temperature above freezing with a small heater in a shaded storage area. If you need extra assurance, this approach provides peace of mind when you reassemble in spring. When you reconnect, check the spark plugs and seals, verify oil level and gear grease, then reattach the prop shaft and test the gear shift for smooth operation that first time you start.

GetMyBoat Winterization Plan for Outboard Motors

Directly drain gasoline from the tanks into a bucket, add marine-specific fuel stabilizer, and fill with stabilized gasoline for storage. Run the engine briefly to distribute the additive, then shut down. This piece of the plan minimizes varnish and gum in the fuel system and keeps fuel delivery reliable when bringing the boat back into service.

Inspect moving parts such as spark plugs, fuel hoses, clamps, and the impeller. Inspect cooling passages, water pump, and thermostat; theres no room for guesswork, so note wear and plan replacements. Do this inspection thoroughly and properly, as common failure points hide in hoses and clamps throughout the system.

Flush cooling lines with fresh water and collect the runoff in a bucket. Inspect hoses for cracks and replace any worn plumbing. Make sure there is no siphon or leak going into the engine space, and ensure the drain path directs water away from moving parts and electricals.

After the engine cools, apply fogging oil into the spark plug holes to coat cylinders. Then spray a thin coat of corrosion-inhibiting solution on exposed metal and the exterior of the block, and rotate the drive shaft by hand to spread lubricant through the gears.

Disconnect the battery, clean terminals, and store it in a dry, covered area. Keep it charged with a trickle charger if possible to prevent sulfation. During storage, attention to wiring integrity and moisture control helps prevent corrosion and intermittent failures.

During storage, support the propulsion unit with a padded cradle or stand, and keep it covered to minimize dust and moisture. Move with care; use straps or chocks and avoid tipping. Keep it upright to protect seals and bearings during moving and in transit.

After every major step, check for leaks along the fuel plumbing and around the water pump. Make an additional maintenance list of parts that require replacement in the coming season, and order them now to prevent delays. This keeps attention on the common failure areas when you bring the system back into service.

Now for additional notes: store in a dry area with stable temperature; this helps prevent corrosion throughout the system. Remember to label each piece and keep spare parts within reach. Maintain a routine that covers every component–from tanks and hoses to the prop shaft–to ensure long-term reliability in marine-specific conditions.

Check the Engine's Manual and Model-Specific Winterizing Steps

Follow the engine's manual exactly to identify model-specific winterizing steps, including the flushing procedure, washdowns, and the exact locations of intakes and block plugs.

Prepare a ready kit: flushing device, spray lubricant, corrosion protection, and clean rags; the manual contains the model's sequence, so read it carefully to avoid problems and to ensure you perform each critical action.

Check for degradation and corrosion by inspecting terminal connections, replacing worn seals, and greasing fittings to keep them greased; this very approach reduces rust risk and minimizes repairs.

Tips for storage: perform flushing and washdowns, spray protective coating on exposed metal, and ensure the block and intakes are clean before cold storage; experienced boaters follow these steps to avoid forgetful mistakes and save money, gaining peace of mind.

If you encounter unusual issues, note them as an idea for future maintenance; following model-specific instructions and keeping a log helps ensure readiness and protects the engine during the cold season, ensuring you are ready to restart with minimal problems in spring.

Stabilize Fuel and Fill the Tank to Prevent Condensation

Fill the tank to full capacity with fresh gasoline and add high-quality fuel stabilizer per label directions. This minimizes residual air space and reduces condensation risk as temperatures drop. Use a bucket to measure the stabilizer dose, then pour it into the tank and circulate it by running the engine 5–10 minutes. Inspect every part of the plumbing and gearcase lubrication paths for leaks, and ensure the vent is properly closed before storage in freezing conditions.

Keep the tank near full whenever possible; down to the last inch of air reduces moisture intake. If you dont fill completely, aim for at least 90 percent capacity and adjust the stabilizer dose accordingly. The idea is that stabilized fuel contains corrosion inhibitors and minimizes moisture retention; their plumbing and lines should be sealed to prevent water entry. After fueling, check the tank cap seal and wipe away any freshwater traces around the fill neck to avoid contamination. Additional measures include ensuring replacement parts are ready if clamps or hoses show wear, and making sure the boat is ready for long storage.

Fog the Engine and Protect Internal Components

Fog the engine by introducing a high-quality fogging oil into each cylinder via the spark plug holes after shutdown; crank briefly to distribute the oil and coat the pistons, rings, and valve faces to prevent moisture buildup and corrosion. Do not forget to disconnect the ignition before spraying so you don’t crank the motor with the spray present. This step matters for engines that sit for months, and the coating helps protect components across most configurations.

Drain the fuel system where feasible: draining hoses and bowls, then add fuel-stabilizing additive in the amount specified by the product, using fresh fuel. Run the engine briefly to circulate stabilized fuel through the lines and reduce contaminants in stored conditions, helping protect systems from varnish and gum.

Inspect and protect plumbing and hoses: replace cracked lines, secure clamps, and seal ports to limit moisture entry. Ensure the cooling and lubrication systems are drained or stabilized, and position drains so liquids cannot backflow. Use clean, high-quality components to minimize contaminants during storage.

The idea behind this approach applies to types of engines alike: prepare, protect, and store. For boaters, keeping fresh fuel, limiting moisture, and reducing contaminants matters. If you have multiple systems, the procedure remains consistent: fog, stabilize fuel, drain as needed, and secure hoses and plumbing to guard against corrosion while stored.

Drain Water, Disconnect Battery, and Protect Electrical Systems

Drain water directly from cooling passages by removing the lower-unit drain plugs with the engine cold; then tilt the outboards to gather any remaining liquid and drain until the water jacket runs dry.

Disconnect battery by removing the negative terminal first, then the positive; lift the battery from its tray and store separately in a dry, ventilated area; if you must leave it on board, attach a maintenance charger and keep terminals insulated to prevent shorts.

Protect electrical systems by cleaning and drying all connectors, applying corrosion-inhibiting products to exposed metal where connectors are exposed, and placing dielectric grease on spark-plug boots and relays; cover steering wiring and control leads to minimize moisture exposure.

Washdowns and hull care: rinse the vessel with fresh water to remove salt and grime, then dry thoroughly; gather hoses and spray fittings, store these items separately from the battery area to reduce corrosion risk.

Fuel management: top off the tank and add marine stabilizer products to keep fuel stable; fuel may expand with temperature shifts, so keep the tank full to minimize expansion and air space.

Storage and checks: store outboards in a clean, dry, covered location until spring; prevent moisture intrusion with protective covers and ventilation; do not start the engine again until a full inspection and system check are complete. This approach is very protective for the steering gear and hull.

Boaters may bring a thorough check to a service professional; a quick, safe wrap provides long-term protection for the flywheel, starter, and charging system, keeping everything ready for spring.

Flush and Lubricate the Lower Unit, Then Store Properly

Begin with a freshwater flush through the line using a marine-grade adapter to remove salt, minerals, and debris. Through-flows help prevent corrosion and gearcase damage; avoid aggressive washdowns that can push grime into seals. After flushing, drain any rinse water thoroughly.

1. Drain and inspect: remove the drain plug and allow the gearcase to drain completely; wipe the area clean. Look for water in the oil; a milky appearance indicates moisture and a potential seal issue to address before storage.
2. Lubricate and fill: install fresh gearcase lubricant that meets the manufacturer’s spec and fill until the level reaches the indicated line or until oil begins to emerge from the vent; reinstall the vent screw and torque to spec. This keeps bearings and gears properly lubricated through the storage period.
3. Protect seals and plumbing: apply a thin film of marine corrosion-preventive product on the exterior and around accessible seals; avoid contact with switches and wiring. If cleaners containing ethanol were used, rinse, dry, and ensure no residue remains because ethanol can affect rubber components over time.
4. Propeller and anodes: remove the propeller to inspect the shaft and replace or grease the o-ring; check the anodes and replace if worn; reinstall with proper torque to prevent leaks or damage.
5. Store properly: place the unit in a dry, level space with the lower unit drained and filled as described; in freezing climates, ensure complete drainage and consider heating or insulation to prevent freeze damage. Use a breathable cover and avoid sealed plastics that trap moisture; a protective coating helps prevent corrosion during long storage.