The dinghy’s motor needs winterizing, too.
Although the cooling systems on most outboards are self-draining and therefore require no freeze protection per se, they do benefit from other storage procedures.
For four-cycle engines, gearcase lube should be replaced annually, along with crankcase oil. Even if the motor received little use during the season, the lubricants should be replaced and inspected for water and metal contamination. If either is discovered, the source of the problem must be determined and the problem resolved before the motor is placed back into service.
Raw-water pump impellers should be replaced no less frequently than every other year. The propeller should be removed, inspected for damage, repaired or replaced as needed, and the spline lubricated using the proper type of marine grease. Be certain to use a new cotter pin when reinstalling the propeller nut. Using a grease gun, grease all zerk fittings on the engine; most have two or three. If there is a portable fuel tank that feeds your engine, it’s best stored empty. However, before the fuel is moved from the tank to its winter home, treat it using a quality stabilizer.
Some outboard manufacturers suggest that the fuel be “winter mixed” using a cocktail of additional two-cycle oil, stabilizer and other fuel additives. Check with your manufacturer for specific guidelines. Run the engine on a freshwater flush using “earmuffs” or the manufacturer’s proprietary flushing attachment, for 10 or 15 minutes. Again, depending on the manufacturer, you may be directed to spray fogging oil into the carburetor while the engine is running and/or squirt a small amount of oil into the cylinders after removing the spark plugs (the latter without the engine running, of course). Check the recommendations for your specific engine.
Unless your storage season is less than four months, once you’ve completed these procedures you should empty and properly dispose of any fuel remaining in the built-in or portable fuel tanks (you could give it away to another outboard user who’s planning to use his dinghy through the winter). Keep in mind that today’s ethanol-spiked gasoline doesn’t store well, even when stabilized. Be certain to properly stabilize any fuel you intend to keep.