Draining the cooling lines, clearing the fuel lines and carburetor, fogging the fuel intakes and cylinders, changing the oil and stabilizing the fuel tank are the primary steps for winterizing an outboard motor. Protection from rust and corrosion can also be enhanced by general lubrication and touching up chipped paint.
To properly drain the cooling lines you should flush the engine with fresh water to remove any sediment or build-up in the lines. Immerse the lower unit in a container of fresh water and run the motor for a few minutes then disconnect the fuel line and let it run until it dies. Remove the flush tank and let the water drain out of the pick-up. Open any drain plugs and bump the motor a few times with the starter to eject any remaining water.
Remove the fuel lines, emptied all of the gasoline, from the inside of the motor. Either drain the gas tank or fill it 95 percent full to eliminate space for moisture build-up, and add an appropriate fuel stabilizer for winter.
Remove the spark plugs and spray fogging oil into the cylinders and then replace the plugs. Give a shot of the fogging oil to the carburetor intakes. Finally, drain the oil from the gear case and top it off with fresh oil to prevent condensation build-up.