Four-stroke outboards are by far the most popular on the market. But there's a lot of confusion about how to properly winterize a four-stroke. Let's end it, right now.
1. Give the motor a good freshwater flush. In some cases you'll need set of earmuffs; in other cases, you can thread the hose right into the outboard. Let the water flow for a good five or ten minutes.
Now that she's flushed out we're going to remove the cowl and rinse away any salt buildup that we find inside.
2. Change the lower unit oil. Even if it's fresh you still want to change it, just in case any water got in there, because water can freeze and expand and cause serious damage. (Watch How to Change the Lower Unit Oil)
3. Since the introduction of ethanol, adding a fuel stabilizer for the winter is an absolute must.
4. Hook up the water again and run the motor for a good ten to fifteen minutes, to work the stabilized fuel through the motor.
5. Next, and this is very important: tilt the motor all the way up and all the way down. You want to make absolutely sure that every drop of water is out of the motor. Otherwise it could freeze and break something.
6. Traditionally the next step is to fog the engine. But many tech heads (myself included) believe it's better just to start it every three weeks or so. That way you don't have to fog it.
Can that really be all there is to winterizing a four stroke? Wait a minute, what about... the antifreeze?
Since no water should remain in the engine, which is tilted down to drain, you don't need antifreeze—even though your mechanic might suggest it as a way to give you another bill.