How to Winterize an Outboard Engine

Treat the fuel with marine stabilizer at the dose on the bottle. Fresh fuel is best: if the gas in your tank is more than about a month old, consider using it up or having it removed.

If your tank is an older vented type, top it off to about 7/8 to 95% full to cut down on condensation, leaving room for expansion. Newer sealed (EPA-style) tanks do not need to be topped off. Never plug the tank vent.

Hook up flushing muffs (or use a test tank) and turn the water on fully before you start. Yamaha and Suzuki both say an engine should only be started out of the water on external muffs made for your engine, not on the built-in flush fitting, which is meant for flushing with the engine off. A few other models (some Mercury and Honda outboards) are designed to idle on their flush port; use it that way only if your manual says so. Engines with two water inlets may need a special adapter; ask your dealer. Run the engine at idle (or the fast idle your manual allows) for about 10 minutes so the stabilized fuel reaches the injectors or carburetor. Keep it in neutral and never leave it running unattended.

Check the telltale (the small "pee" stream). If it is weak or missing, shut down and see the overheating guide before going further.

This also warms the oil and gear lube so they drain better.

With the engine warm and upright, drain the oil, replace the filter and refill to the level in your manual. Use marine FC-W oil, not automotive oil.

Make sure the old filter's rubber gasket came off with the filter. A doubled gasket can leak and starve the engine of oil. See the full oil change guide for details.

Change the water-separating fuel filter (in the boat or on the engine) and any on-engine filter that is due. Lightly oil the new gasket. Check for leaks after restarting.

Fuel is a fire hazard: no smoking, no sparks, wipe up spills and keep a fire extinguisher close.

Fogging coats the inside of the cylinders with oil so they do not rust over winter.

• Most 4-strokes and carbureted 2-strokes: follow the can and your manual. Common methods are spraying into the air intake while the engine runs on muffs until it smokes heavily, or removing the spark plugs and spraying into each cylinder with the engine off.
• Direct-injection 2-strokes: use the method in your manual (some use oil through the spark plug holes, some use a storage mode).

If you spray through the plug holes, disconnect the kill switch lanyard so the engine cannot start, then turn the flywheel by hand (in its normal direction only) to spread the oil.

If plugs are due on your schedule, install new ones gapped to spec. A light coat of anti-seize on the threads helps, unless your manual says otherwise. Do not overtighten; check your manual for the torque.

Drain the lower unit through the bottom drain screw and top vent screw. Look at the old lube: creamy or milky oil means water is getting in, and metal chips mean internal wear. Either one is a dealer visit.

Refill from the bottom hole until lube comes out the top, then reinstall the screws with new gaskets. Never leave the gearcase empty over winter. Full steps are in the lower unit oil guide.

Remove the propeller (wedge a block of wood between a blade and the anti-ventilation plate to hold it). Remove any fishing line wrapped near the prop shaft seal; line can cut the seal and let water in.

Grease the shaft splines with marine grease, then reinstall the prop to the torque in your manual, or store it inside to discourage theft. Send out a bent or chipped prop for repair now.

• Power trim fluid: check the reservoir level with the engine tilted as your manual describes. Milky or pink fluid means water contamination; have it checked.
• Anodes: replace any that are about half gone.
• Grease: pump fresh marine grease into every fitting listed in your manual (steering, tilt tube, swivel). New grease pushes out trapped water.

Wash and dry the engine. Spray a corrosion inhibitor over the powerhead under the cowl and on the outside metal parts. Touch up chips in the paint on the lower unit.

Charge the battery fully. Disconnect it (negative cable first) or remove it and store it somewhere cool and dry, ideally on a maintenance charger. Check flooded batteries for electrolyte level and top up with distilled water if needed.

Turn off the water and remove the muffs. Trim the engine all the way down (vertical) and leave it that way so water drains out of the powerhead and gearcase. A tilted-up engine can trap water that freezes and cracks parts. Check that the water intake screens on the gearcase are not packed with mud or debris, so the water has a way out.

If the boat is stored outside, Yamaha suggests that once the lower unit is fully dry, a tightly sealed plastic bag over it helps keep rain and snow out. Remove it in spring.

Cover the engine. Some owners put dryer sheets under the cowl to discourage mice; leave yourself a note to remove them in spring.

Log the date, engine hours and what you did (oil, filters, gear lube, plugs). It makes spring commissioning faster and helps when you sell the boat.