When it comes to storing your gasoline engine—whether it’s an inboard, outboard or I/O—for long periods, preserving the fuel and protecting the engine’s internal components from corrosion are the 2 main goals. After you’ve run conditioned/stabilized fuel through the engine, the next step is protecting the engine’s cylinders and other internal spaces where moisture can accumulate and cause rust and corrosion during layup.
It’s important to note that different types of engines (eg., 2-stroke, 4-stroke, EFI, DFI) have different storage requirements. Always check with the manufacturer to find out what they recommend for your specific make and model of engine. If you’re unsure, you’re better off taking your engine to a qualified marine mechanic or dealer. The procedures outlined below are general recommendations only, and may not be right for your engine.
If you have an older carbureted engine, you can protect it by spraying fogging oil directly into the carburetor(s) and cylinders. Some mechanics recommend spraying the fogging oil into the air intake while the engine is running at idle or just above idle so the oil can work its way through the carburetor(s), cylinders and exhaust system. If you go this route, you may need to adjust the throttle to keep the engine from stalling as you introduce the fogging oil. When thick, blue smoke begins billowing out of the exhaust, idle down and keep spraying fogging oil into the air intake until the engine stalls.
Now remove the spark plugs and spray fogging oil directly into each cylinder via the plug sockets. Replace the spark plugs, tighten them to spec, and rotate the flywheel to spread the oil over the cylinder walls. You can rotate the flywheel manually or by “bumping” the ignition key. In either case, make sure the plugs wires are disconnected so the engine will not accidentally start.
Another method of fogging the engine is to open the carburetor(s) manually and spray fogging oil directly into the carbs while the engine is shut down, then remove the spark plugs and spray fogging oil into each cylinder. (If you need to replace the plugs, wait until spring and after you’ve burned the fogging oil out of the cylinders.)
Install the spark plugs and rotate the flywheel manually or by turning the ignition key to distribute oil throughout the cylinders. Again, make sure the plugs wires are disconnected before you do this.
With a direct-injection engine, fogging is not recommended. The engine manual for a 2004 200-hp Mercury OptiMax DFI outboard recommends removing the spark plugs and introducing 30 milliliters of 2-stroke DFI engine oil directly into each cylinder via the plug sockets.
By the way, once you’ve removed the spark plugs, check the tips for signs of wear. If the electrodes show heavy, black carbon buildup, the engine could be getting too much oil; if tips are white and chalky, the oil mix may be too lean. In either case, have your mechanic or dealership check it out.
Once oil has been added to each cylinder, install the spark plugs and tighten them with a torque wrench, but do not reattach the wires. Manually turn the flywheel several times to distribute oil throughout the cylinders.
Lastly, place a dollop of dialectric grease on each end cap of the spark plug wires and attach them to the plug terminals.
Content extracted from http://newenglandboating.com/winterize-it-outboardio-cylinder-protection-2/