Winterizing Your Outboard Boat: A Step-by-Step Guide

STEP 1 - Stabilize the fuel

Gas left sitting for months breaks down and turns gummy, and ethanol blends pull in moisture.

• Fill the tank to about 95% (not empty - an empty tank collects condensation; not 100% - fuel needs room to expand).
• Add fuel stabilizer at the dose on the bottle.
• Run the motor for several minutes with water flowing (on muffs or in a test tank) so treated fuel reaches the lines and injectors or carburetor.
• Replace the fuel filter and any fuel/water separator.

Pro tip: On a carbureted motor, drain the carburetor float bowl as your manual describes.

STEP 2 - Flush with fresh water and let it drain

Salt, silt and minerals left in the cooling passages corrode the engine over winter.

• Flush the cooling system with fresh water using muffs and a hose (essential if you boat in salt or brackish water).
• Let all water drain out completely.
• Wash the outside of the motor with soap and water, rinse well, and add a light coat of wax.

Pro tip: Never run the motor without water flowing to it - the water pump impeller can be destroyed in seconds.

STEP 3 - Fog the engine

A thin coat of fogging oil protects pistons and cylinder walls from rust while the motor sits.

• Spray fogging oil into the cylinders following your manual (often into the air intake while running, or into each spark plug hole).

STEP 4 - Change the engine oil (4-stroke motors)

Used oil holds acids and moisture that sit against internal parts all winter. Fresh oil stores clean.

• Run the engine briefly first so the oil drains easily and carries contaminants out.
• Change the oil and filter, then check the new filter for leaks.

Note: 2-stroke outboards don't have a crankcase oil change - skip this step.

STEP 5 - Change the lower-unit gear lube

The gearcase is the lowest point of the motor. Water that gets past a worn seal settles there, freezes and can crack the housing.

• Remove the drain screw and let the gear lube drain.
• Look at it: milky or creamy lube means water got in - have the seals checked before next season.
• Refill with fresh gear lube, pumping it in from the bottom hole until it comes out of the top vent hole. Then reinstall both screws.

STEP 6 - Grease and protect the propeller shaft

Prevents corrosion and lets you catch damage early.

• Remove the propeller and check the shaft for wrapped fishing line, which can damage the seal.
• Coat the shaft and threads with water-resistant marine grease, then reinstall.
• Grease the motor's other fittings per the manual.

STEP 7 - Store the motor tilted DOWN

Stored upright (vertical), any water left in the motor drains out instead of pooling in the gearcase and freezing.

• Lower the motor fully before you walk away for the season.

STEP 8 - Drain the boat's own water systems

Livewells, baitwells, washdown pumps and freshwater lines freeze just like the engine.

• Drain each system and run each pump dry for a few seconds.
• Where lines can't be fully emptied, run non-toxic (pink, propylene glycol) antifreeze through them. Never use automotive antifreeze.
• Empty, clean and dry the bilge. If you can't get every drop out, add a small amount of non-toxic antifreeze.

STEP 9 - Pull the hull drain plug

Rain and snowmelt drain away instead of pooling and freezing in the bilge.

• Remove the drain plug for storage on land.

Pro tip: Clip the plug to your ignition key or steering wheel so it goes back in before launch.

STEP 10 - Charge and disconnect the battery

Batteries slowly drain even with everything off, and a discharged battery can freeze; a fully charged one holds up far better in the cold.

• Fully charge the battery.
• Disconnect the negative cable first, then the positive.
• Ideally, take the battery home and keep it on a smart maintainer somewhere dry.

STEP 11 - Clean and dry out the interior

Damp gear under a cover turns into mold and mildew.

• Take life jackets, cushions, towels and lines home, or stand cushions on their sides to air out.
• Inspect and test safety gear (life jackets, fire extinguisher, flares) and electronics; replace anything that isn't working.
• Leave a moisture absorber aboard, and add rodent deterrent - a covered boat is an inviting nest, and mice chew wiring and upholstery.
• Clean the hull, especially the bottom. Growth and scum wipe off easily in the fall but dry hard over winter.

STEP 12 - Cover the boat

Snow is heavy. A flat cover collects water, sags and tears.

• Use a fitted storage cover or professional shrink-wrap (shrink-wrap seals out moisture and pests better than a tarp).
• Prop the cover with a pole or frame so it peaks and sheds snow.
• Make sure it's vented so trapped moisture can escape.