Flush the cooling system, drain the fuel, change the oil, lubricate the engine and propeller shaft and stabilize the fuel supply to winterize an outboard motor on a boat. Some steps may vary depending on the make and model of the outboard motor, but the basic procedure is the same.
Connect a flushing attachment to the fresh water intake, and attach a garden hose to the port on the flush kit. Turn the motor on, and let it run long enough to thoroughly flush the cooling system. The time needed varies depending on whether the motor was used in fresh or saltwater. Saltwater causes more buildup and needs longer to fully flush.
Let the engine continue to idle, and turn off the fuel supply or disconnect the fuel line from the engine. Before the engine runs out of fuel and dies, spray fogging oil directly into the carburetor. When the engine dies, all of the fuel has been cleared out. Change the engine oil as well as the oil in the lower unit gear box. Use a grease gun, and insert grease into all of the grease zerks and linkages.
Fill the fuel tank at least 95 percent full of fresh fuel so there is less room to gather condensation inside of the tank, and add a good fuel stabilizer to the tank for winter.