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Outboard Winterization

The transition from balmy summer days to the crisp autumn air signals more than just a change in seasons for boat enthusiasts. It's a reminder of the crucial task that lies ahead: outboard winterization.


While many might be tempted to simply dock their boats and forget about them until the next boating season, experienced mariners know that this is the prime time to invest in the longevity and health of their outboard motors. Preparing your motor for the cold months not only prevents potential damage from freezing temperatures but also ensures that come spring, your boat is ready to hit the water running, rather than stalling at the dock.


Dive into our comprehensive guide on outboard winterization and discover the key steps to keep your boat in pristine condition during its winter hibernation.



Step 1: Fill the Fuel Tank

Fill your fuel tanks. Fuel tanks that are not full allow for condensation to form on the tank walls during the winter months, and this condensation will introduce water into your fuel supply. We recommend the fuel tanks be kept at least 3/4 of the way full.

Step 2: Fuel Stabilizer:

Once the tanks are filled, add fuel stabilizer to your gasoline or diesel fuel tank. The amount added is based on the tank size, so be sure to read the directions and add the proper amount. Also be sure to use the proper fuel stabilizer for your fuel type, as gasoline and diesel fuel stabilizers are very different in both their chemical makeup and effect.


Gasoline fuel stabilizer prevents gumming or varnishing of the fuel through the engine system, prevents rust by displacing water, and helps prevent the separation of ethanol in the gasoline. Fuel stabilizer, such as Sta-Bil, is compatible with both ethanol and non-ethanol gasoline, and stays effective for roughly 2 years.

Engine Flushing

Once the fuel system is stabilized, we recommend running the engine for an extended period of time, using freshwater to flush the cooling system. By running the engine, the stabilized fuel will have the chance to run through the fuel system and also allow for easy removal of the engine oil.


Step 3: Antifreeze Flush

Many smaller outboards are self-draining, but we find that flushing the engine with antifreeze is a great measure to add extra protection during the winter months. To flush the engine with antifreeze, we use a large buck with a garden hose valve on the bottom. We connect the bucket to the engine muffs and continue to run the engine until we see antifreeze coming from the outboard telltale.


Alternatively, using compressed air to blow out the raw water-cooling system via the engine flush connection is another commonly practiced technique, but we do find antifreeze to be more reliable.


Step 4: Engine Fogging

Once your engine has been thoroughly flushed with antifreeze and up to temperature, we recommend using a fogging spray to protect your engine internals. Fogging spray works by coating the inside of your engine and cylinders with a thin film of oil, prevent moisture in the air from causing corrosion.


To fog your motor on carbureted motors, remove the air intake and spray the fogging solution directly into the engine. During this process, excessive smoke will be emitted from the engine exhaust, and the engine may start to run roughly - which is all normal. Is the engine does not stop due to the fogging, immediately turn the motor off.


On fuel injected outboards, or once the fogging is complete on carbureted models, it is recommend removing the spark plugs to and spraying fogging solution directly into each engine cylinder to ensure full protection. While the spark plugs are removed, please do not be tempted to replace the sparks. Spark plugs can be fouled by the process of burning off the fogging solution during spring commissioning. During spring commissioning, we recommend waiting until the engine is no longer producing excessive smoke before changing your spark plugs.


Step 5: Engine Oil

Once the engine is warm, and the engine is fogged, it is time to change the engine oil. Engine oil can be removed through a drain plug if available, or by using a vacuum fluid extractor through the dip stick hole. Make sure to do this process while the engine is still warm, cold oil becomes very viscous, and the removal process can be long and difficult.


Once removed, inspect the oil for milkiness or contamination. If any of these symptoms are present, it is best to call a marine outboard mechanic to further diagnose the issue, so it can be resolved over the winter. We highly recommend not waiting to address any found issues during the spring, as most marine service providers are in high demand, and often scheduled more than a month out due.

Once the oil is removed from the engine, change the oil filter before refilling the engine. It is often helpful to lay a rag below the oil filter, as they are often mounted vertically and can spill oil into the cowling during removal. Once replaced, we are always sure to date the outside of the filter with a permanent marker to prevent any questions in the future.


With the filter replaced, refill the oil to the manufacture recommended capacity with the recommended oil type. To prevent overfilling, we often add slightly less oil that the recommended capacity at first and checking the dipstick before adding the final amount.


Engine oil should always be replaced during winterization, as engine oil will become acidic after prolonged use, causing internal corrosion and potentially shortening the lifespan of the motor.


Step 6: Lower Unit Oil

Just as with engine oil, it is highly recommended to change your lower unit oil out during the winterization process. To drain the lower unit oil, you must start by removing the lower drain bolt first with a large flathead screwdriver, followed by the upper drain screw. By removing the top bolt last, the oil will be less likely to pour out of the hole, preventing you from accidently losing the bolt and making a mess.


As with engine oil, it is important to inspect the oil as it comes out. If the oil is milky, we highly recommend replacing the crush washers on both upper and lower bolts.


During the refill process, we recommend using a lower unit pump to fully fill the lower unit with oil. To start, connect the pump fitting to the lower drain hole, and pump until the oil flows unmediated from the top hole.


Before removing the pump from the upper lower drain, replace the upper drain bolt and tighten it down securely. This process will prevent oil from rapidly draining during the pump disconnection process.


Step 7: Propellers and Hub

The winterization process is a great time to check you propeller and hubs for damage. Remove the propeller, and check for any fishing line that might have wrapped around the shaft. Contamination around the shaft has the possibility cause seal failure, so catching any issues as soon as possible is extremely important. Be sure to grease the shaft before reinstalling the propeller.


Step 8: Storage

After work is completed, your outboard motor should be stored in the downward position to prevent water from pooling in the motor cowling.





Side Note 1: Carbureted Motors

During winterization, if the motor is carbureted, it is important to drain the fuel bowl to prevent varnishing of the fuel. On smaller motors, it is also recommended to run the engine dry, with the fuel shutoff switch engaged, to prevent any fuel from varnishing during storage.


Side Note 2: 2-Stroke Motors

Winterization for 2-stroke motors is identical to care of 4-stroke motors, with the exception to the motor oil and filter.



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