Winterizing a 4-stroke Outdrive

Modern 4-stroke outboard boat motors, like other modern appliances and technology are more complex than their earlier counterparts. Modern outboard engines can cost as much as an automobile, so to make sure it lasts as long as possible, you need to take good care of it, especially prior to a winter layup. The advanced technology that goes into newer 4-stroke engines makes them more responsive and powerful, but also more delicate and needy when it comes to precise care. With the proper care your outboard boat motor will last a long time.


Engine muffs
Water hose
Fogging oil
Spark plugs
Engine oil
Paper bag
Plastic tie
Water resistant grease


Remove the safety lanyard from the ignition so the engine cannot start accidentally. Take off the propeller and check it for nicks and dents.

Use a pair of engine muffs hooked up to a water hose to provide fresh water to the engine. Make sure the water intake holes on either side of the lower unit are completely covered by the muffs. Start the engine and run it long enough to completely flush the system and let the engine warm up to operating temperature.


Disconnect the battery and clean the terminals. Store your batteries in a warm, dry place away from any flames. Remove the spark plugs and spray fogging oil into the cylinder. Rotate the engine a ½ turn each time you spray oil into the cylinder. Replace sparkplugs with new ones for the next season. Coat the entire power head with corrosion protection oil.

Check your engine’s specific manual for instructions on the location of the lower unit oil drain plugs. Unscrew both of the two drains to allow the oil to drain. Pump the fresh oil recommended by the manufacturer of your engine into the lower oil drain to change the oil in the lower unit. Fill with fresh oil until it appears from the top drain hole.

4-stroke engines require the oil in the crankcase replaced as well. Open the drain in the upper engine compartment and let it drain out. Much easier if the engine is still warm and the oil is not thick. Replace with the proper oil type for your specific engine.

Remove the gas line and drain as much as possible from the carburetor. Store your hoses and lines where varmints can’t get at them, and keep them out of direct sunlight. Place them in a dark bag and throw a single fabric softener sheet in with it for the best protection from mice and rats.

Add a fuel stabilizer to your gas and fill the tank to the top. Keeping a full tank of gas eliminates the possibility of condensation in the tank that will harm your engine in the spring.


Grease all zerks, nuts, bolts, joints, and other moving parts. Apply a generous amount of water resistant grease all over the propeller shaft and cover with a bag secured with a tie.

Position the engine in an upright position for storage. Do not leave it up over the transom in the trailering position. That is hard on the transom of the boat, and may allow water to pool inside. Any water left inside the engine can freeze and burst lines, or crack the engine block.

Don’t cover your engine with air-tight fabrics. Putting the shrink-wrap, or other heavy canvas covers used to protect the deck and cabins of the boat over the engine cowl is a common mistake. In fact, sealing it air-tight creates condensation that is disastrous. Your outboard is well-equipped to handle the weather around it as long as you take care to protect the inside of it.