Outboards stored over winter without preparation can suffer from stale fuel, corrosion and frozen water in the cooling passages or gearcase. These are the standard steps; always follow the procedure in your motor’s owner’s manual, which takes priority.
1. Stabilize the fuel
Add a marine fuel stabilizer to the tank at the recommended ratio and run the engine long enough for treated fuel to reach the fuel system. Some owners of carbureted motors run the carburetor dry instead; check your manual for which approach applies to your engine.
2. Flush the cooling system
Run the motor on fresh water with flush muffs or the flushing port to remove salt and silt, then let it drain completely with the motor vertical.
3. Fog the engine
Where the manufacturer recommends it, spray fogging oil into the intake (or cylinders) to coat internal parts against corrosion.
4. Change the gear oil
Drain the lower unit gear oil and refill with fresh oil. Milky oil is a sign water has entered the gearcase and the seals should be checked before spring.
5. Grease, inspect and protect
Grease the fittings, check the propeller and its hardware, touch up chips in the paint, and inspect the anodes.
6. Store it properly
Disconnect and charge the battery, store the motor upright so water drains out of the cooling passages, and cover it.
Winterizing the rest of the boat
- Water systems: drain livewells, baitwells, washdown and freshwater systems, and use non-toxic marine or RV antifreeze where water could be trapped.
- Bilge and hull: pump and dry the bilge, clean the hull and deck, and open lockers so the interior can dry and resist mildew.
- Batteries: charge cranking and trolling motor batteries, disconnect them or remove them for storage, and keep them on a maintainer or check them every few months; lithium batteries are best stored partly charged, see how long do lithium batteries last.
- Inboard and sterndrive engines: these need their own procedure, usually draining the block or filling it with antifreeze, so follow the engine maker’s manual.
- Cover: use a fitted cover or shrink wrap with ventilation so moisture can escape.
- Trailer: check the tires, wheel bearings and lights, and keep the boat level so rain drains.
The gear oil step is covered in detail in how to change lower unit oil.
Replacing a motor rather than storing it? Browse outboard motors by horsepower. See also: outboard shaft length guide · 4 stroke vs 2 stroke outboards · outboard motor maintenance.
More guides: outboard won’t start in spring · milky lower unit oil · outboard won’t idle after storage · how to flush an outboard · boat battery dies over winter · ethanol in boat fuel and stabilizer · how to change outboard oil · outboard steering cable · tilt and trim fluid · zinc vs aluminum anodes · lithium batteries in cold weather.
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