Four-stroke outboard engines are by far the most popular on the market. But there’s a lot of confusion about how to properly winterise them. Here's our step-by step guide with Lenny Rudow.


The basics of winterising your outboard

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.

3. Since the introduction of ethanol, adding a fuel stabiliser for the winter is an absolute must.

4. Hook up the water again and run the motor for a good 10-15 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.

Outboard winterising tips

Don't mummify your outboard engine

I spotted this outboard engine last year (see photo) wrapped in an old shower curtain. At least this owner didn’t go all the way and seal the plastic with duct tape.

Wrapping an outboard engine in plastic

Wrapping an outboard in plastic is asking for corrosion trouble under the cowl.

When you wrap an outboard in plastic you ensure that any moisture that’s under the cowl, or gets under the cowl, cannot escape through the vents in the cowl provided just for that purpose. This moisture, even if it’s just condensation, can start corrosion on electrical connections and moving parts like the throttle linkage. During the course of the winter there will be cold days and warmer days, the sun may shine on your motor, and the air under the cowl will need to breathe.

• Bonus tip: Before laying up the engine spray down the powerhead with a water-displacer like WD-40. Then secure the cowl but don’t cover it.

• Bonus tip: If you have your boat shrink-wrapped either don’t cover the outboard, or rig the wrap so that air can still circulate around the motor. And make sure the shrink wrap is not covering the vent of an inboard fuel tank.

Don't tilt the outboard up

One of the great features of an outboard motor is that it’s self-draining, but it’s only self-draining when it’s in a vertical position. If you tow the boat home on its trailer with the engine tilted up and then forget to lower it before storage, any water left in the engine will freeze and could cause damage. Another problematic possibility is that snow or rain water can collect in the barrel of the prop and migrate down into the exhaust passages of the gear case. Eventually it gets really cold one night and… POP! Your gearcase is cracked. Of course, this couldn't happen since you wrapped your motor in plastic and sealed it with duct tape… never mind.

Remove the propeller

If the boat is stored outdoors, you might as well put a sign next to it that reads: “Steal My Propeller.” Besides, you’ll want to pull that prop so you can check the shaft for wrapped-up fishing line and remove it before it cuts through the prop-shaft seal and lets water into your gearcase.

fishing line around a prop shaft

Use your finger nail or a sharp pick to check for fishing line around the shaft at the seal. It’s often embedded in grease and hard to see.

Maybe the prop-shaft seal is already damaged. Well, now you know. Get it fixed over the winter when business is slow at the repair shop. The last step: slather that exposed shaft with some grease so it doesn’t corrode over the off-season.

• Bonus tip: If your back-up engine is small enough to carry, then unclamp it and put it somewhere secure. I keep mine in my office, so I can enjoy that outboardy smell all winter.

Don't dry-start the engine

I know your outboard sounds really cool when you start it up on the trailer, but there's no reason to start the engine without first attaching a supply of water – as per the instructions in your owner’s manual. Remember: your outboard is self-draining. Starting the engine to “blow out the water” even for just a few seconds can seriously degrade or destroy your water pump impeller, which relies on water for lubrication. If you really can't go without hearing that noise, get yourself a ride-on lawn mower. They're usually air-cooled!

Written by: Charles Plueddeman
Charles Plueddeman is's outboard, trailer, and PWC expert. He is a former editor at Boating Magazine and contributor to many national publications since 1986.