How to Winterize an Outboard Motor

Winterizing is an essential process for protecting outboard motors stored in climates that experience freezing temperatures. In fact, winterizing is recommended for all outboard engines that remain unused for months. 

Mercury outboard winterization products

Think of winterization as "extended storage protection". A motor that isn't winterized can quickly deteriorate, inside and out. Stale fuel, old engine oil, and unflushed deposits can easily damage your outboard if not dealt with before a long period of inactivity. 

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You can pay a local marina or boat mechanic to winterize your outboard motor, but it won't be cheap. The sensible alternative is to do it yourself. Winterizing can be done with a handful of fluids and lubes, and without any special tools. Here are some ways to winterize an outboard engine.

Flush and Drain the Cooling System

Salt and other contaminants generate corrosion and blockages within your outboard's cooling channels. Using water muffs, run the outboard and flush the motor with fresh water for several minutes to remove all deposits from the cooling system.

If you use your outboard in salt water, run and flush it for at least 10-15 minutes. Once the engine is flushed, let it drain out. If any water is left in the powerhead or water lines, it could easily freeze and cause damage to the engine over the winter. Do a final engine flush using marine antifreeze so that any traces of liquid left behind won't actually freeze.

Change the Engine Oil and Filter

Old engine oil slowly breaks down, and releases acids and other impurities when left stagnant over long periods of time. These acids corrode and pit vital precision components within the engine. Old oil also contains tiny metal fragments that cause additional wear to the inside of the motor. 

Winterize outboard engine oil change

Run the engine for a couple of minutes to warm the oil so that it drains faster and removes as many impurities and fragments as possible. Refill the outboard with a quality marine engine oil, and change out the oil filter while you're at it.

Change the Lower Unit Oil

Replace the old gearcase oil in the lower unit for the same reasons you would change the engine oil. Drain and replace the gearcase lube with a fresh supply. When changing the gear oil, be sure to check for moisture. If the old gear lube is milky, it's an indication that water is leaking into the lower unit. The leak must be found and fixed (it's usually a failing gasket or seal) before replacing the gear oil.

Fog the Engine and Empty Fuel Lines

When an outboard sits idle, the oil coating the internal surfaces gradually drains down to the bottom, leaving metal surfaces exposed to moisture in the cold air that can corrode the engine.

Winterize an outboard fogging oil

Any un-oiled metal parts will also scuff against one another when the engine starts, causing more internal damage. Fogging oil keeps all the metal surfaces in an outboard properly coated and protected when it's not in use. 

Yamalube fogging oil

Mercury QuickStor fuel stabilizer

Stale fuel left in fuel lines, carburetors or fuel injectors will evaporate and leave behind gummy, varnish-like deposits that can easily block the carbs or injectors and prevent proper fuel flow through the lines. Remove the engine's air filters to access the motor's air intakes, then remove and plug the fuel delivery lines. Start the outboard and spray fogging oil into the air intakes as it runs to coat the inside of the motor. Continue running the motor until it shuts off, so you know all the fuel has been emptied from the carbs or injectors and fuel lines.

Lastly, remove the spark plugs from the powerhead, and spray more fogging oil into the holes to coat the interior of each cylinder. Turn the engine over with the starter a few times to coat the fogging oil over the walls of the cylinders. Replace the spark plugs with a new set.

Fill the Fuel Tank and Stabilize the Fuel

The inside of metal fuel tanks is prone to corrosion by moisture trapped in the cold winter air. Ethanol fuels attract tiny water molecules, which over time separate from the fuel and begin corroding the insides of the fuel system.

Winterize an outboard add fuel stabilizer

To prevent water corrosion within your fuel tanks, fill them to the brim with fresh marine fuel, leaving no areas exposed to the air. Filling the fuel system also prevents gaskets and O-rings from drying up, as well as water accumulation.

Marine fuel doesn't contain ethanol, so water molecules are not attracted to it and water doesn't build up within it. If you can't find marine fuel, fill up with regular ethanol fuel and treat it with a marine-grade fuel stabilizer. Fuel stabilizers prevent water from forming, and stop the fuel from breaking down and leaving behind varnish-like deposits. Don't forget to replace all the fuel filters and the water-separator filter when winterizing your outboard motor so the entire fuel system is in perfect shape for storage.

Winterize outboard motor fuel filter water separator

Grease and Oil the Powerhead and the Trim & Tilt

If your outboard has any grease fittings, make sure they're freshly greased. The steering and trim & tilt mechanism usually have grease zerks that need repacking. Grease the propeller, prop shaft and any exposed shaft splines with marine greaseSpray the powerhead with a light oil so all exposed metal parts are protected from the elements. Or use an oiled rag and wipe down the exterior of the powerhead and any external metal components.

Clean the Engine Cowling

Wash the engine cowling and give it at least two coats of marine wax to protect it. Touch up any paint chips, and replace faded or missing decals. Finally, cover the engine to prevent moisture from getting to it and ice from forming upon it. And that's it, your outboard motor winterizing is complete.




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