How to Winterize Your Outboard Motor

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After a magnificent summer of boating, winter is fast approaching and the time has come to winterize your outboard motor for the long winter months to come. Correctly preparing your motor for winter storage is necessary to prevent damage from freezing temperatures and to ensure that your motor is ready to go when spring arrives.

Now is a good time to reference the owner’s manual provided with your motor. If you do not already have one, it is also a good idea to purchase a shop manual that covers your outboard motor.

Tools and Supplies

Before beginning the winterizing process, gather the necessary tools and supplies. The following list shows the tools and supplies necessary.

  • Engine oil and filter (four-stroke models)
  • Fuel filter
  • Fuel stabilizer
  • Water resistant marine grease
  • Fogging oil
  • Gearcase (lower unit) lube
  • Rust inhibitor spray
  • Spark plugs
  • Basic hand tools
  • Grease gun
  • Spark plug gap tool (feeler gauge)
  • Gear lube pump
  • Motor flushing device
  • Socket for the propeller nut
  • New gaskets for the engine and gearcase drain plugs


Perform an overall inspection to identify excessively worn or damaged components. Check the wiring for loose connections and damaged or worn insulation. Inspect the wiring connectors for loose contacts, damage or corrosion. Also, look for obvious fuel or oil leakage.

Sacrificial anodes installed on the motor prevent corrosion to the powerhead and cooling passages. The anodes are made of a material that is more corrosively active than the powerhead and other components. The anodes, therefore, sacrifice themselves to protect other parts of the outboard motor. Inspect the sacrificial anode for excessive wear. Replace any anode that has lost 1/3 or more of its material. Use a stiff brush to clean deposits or other material from the anode. If replacing the anode, thoroughly clean its mounting surface so the anode mounts to a clean, bare metal surface.

Some models are equipped with a ground wire attached between the anode and metal part of the motor. Inspect the ground wire for looseness or corrosion and repair as necessary. Never paint a sacrificial anode

Carefully inspect all fuel hoses for leakage, wear or damage. Make sure all fuel hose connections are secure and tight.

Thoroughly clean the entire motor using mild soap and pressurized water. To prevent water intrusion, do not direct high-pressure water toward any openings, seals, plugs wiring or wiring connectors. After cleaning, spray or wipe all external surfaces with a suitable anti-corrosion spray.

  • Star Brite Ultimate Corrosion Blocker Plus
  • Sta-Bil Corrosion Inhibitor
  • WD-40
  • West Marine Salt Off Spray
  • CRC Marine Heavy Duty Corrosion Inhibitor
  • Q Maxx SALT Inhibitor.

Stabilize the Fuel

Add fuel stabilizer to your tank to prevent gum and varnish from forming in your tank during storage. Gasoline begins to degrade after as little as 30 days. As a result, gum and varnish start to form in your tank. You can help prevent hard starting and poor performance after storage by treating the gasoline prior to storage. Follow these steps to treat your fuel.

  1. Always try to run your tank low on fuel so you can refill with fresh fuel. Use premium gasoline with an octane rating of 89 with no more than 10 percent ethanol content. Fill the tank to approximately 95 percent full to allow room for expansion. If your gasoline is more than 60 days old, drain and refill the tank.
  2. Follow the stabilizer manufacturer’s directions regarding how much stabilizer to add per gallon of gasoline that you intend to treat.
  3. Add the appropriate amount of stabilizer to the tank.
  4. To prevent damage to the water pump and powerhead, never run the outboard motor without providing cooling water to the powerhead.
  5. Attach a suitable flushing device to the water intake located on the lower unit. Then, connect a hose to the flushing device and water supply. Open the water supply until you can see water escaping from the around the flushing device. After starting the motor, adjust the water pressure so a steady stream of water is flowing from the cooling system pilot hole on the gearcase.
  6. Start the outboard and let it run at a fast idle speed for around 10 minutes to ensure stabilized gasoline has circulated throughout the fuel system and carburetors or fuel injection system. Meanwhile, this process is also flushing the cooling system of salt, sand or dirt.
  7. Prior to shutting off the motor, refer to Fogging the Motor.
  8. Shut off the motor and water supply. Install a new fuel filter and water-separating filter if so equipped.

The following are some recommended fuel stabilizer products:

Fogging the Motor

Fog the outboard motor to prevent rust or corrosion from forming inside the powerhead during the storage period.

Two-and Four-Stroke Models Equipped with Carburetor(s)

Provide your outboard motor with cooling water as described under Stabilize the Fuel. Never start and run the motor without providing cooling water.

With the engine running at fast idle speed, spray a good quality fogging oil into the air intake or carburetor(s). On multi-cylinder models, spray the fogging oil into each carburetor or intake. If the engine dies while spraying the oil, restart and increase the idle speed slightly. Always consult the fogging oil manufacturer’s instructions. Continue spraying until a cloud of white smoke exits the exhaust. Repeat for each cylinder or carburetor.

Two-and Four-Stroke Models Equipped with Fuel Injection

Add one-two gallons of stabilized gasoline to a remote fuel tank. See Stabilize the Fuel. Connect the remote fuel supply to the fuel inlet. Provide the motor with cooling water, start the motor and run at fast idle speed. When you notice white smoke from the exhaust, the motor, shut off the motor and disconnect the water supply. Disconnect the remote fuel tank and reattach the fuel line to the fuel inlet.

Change Powerhead Oil and Filter (Four-Stroke Models)

Most outboard motor manufacturers recommend changing the motor oil and filter at 100 hour intervals. However, it is always good practice to change the oil and filter prior to winter storage regardless of hours since the last change.

Always purchase engine oil specifically designed for marine four-stroke outboard motors. Do not use oil designed for automotive applications. Certainly, a good quality aftermarket marine oil is generally suitable. On the other hand, you cannot go wrong with using oil specifically recommended by the motor manufacturer. Consult your owner’s manual for the recommended viscosity and capacity.

Provide the outboard motor with cooling water as described earlier. Allow the motor to run for 5-10 minutes until it is at normal operating temperature. Shut off the motor.

Oil evacuator pumps are available in either electric or manual pump style. Electric pumps are certainly more expensive. The manual-type pumps work quite well and are perfect for the do-it-yourself boater.

  1. Remove the oil fill cap from the powerhead. Remove the oil drain plug and drain the oil into a suitable container or draw the oil using an evacuation pump following its manufacturer’s directions.
  2. Using an oil filter wrench, loosen and remove the oil filter.
  3. Install a new gasket onto the oil drain plug if removed.
  4. Install the drain plug and tighten securely.
  5. Apply clean engine oil to the filter gasket. Install the filter. Tighten the filter an additional ¾ turn after the filter gasket contacts the mounting surface.
  6. Add the correct amount of oil into the fill hole and install the fill cap.
  7. Start the motor, then check for leakage at the oil filter and drain plug.
  8. Shut off the motor. Make sure the motor is upright and level. Check the oil level to make sure the crankcase is full. The motor must be in a level position or the oil level on the dipstick will be inaccurate. Add oil if necessary, but do not overfill.

Change the Gearcase (Lower Unit) Oil

Refer to your owner’s manual for the recommended viscosity and quantity of gear lube. Most manufacturers recommend synthetic gear lube for late model high-performance motors.

Purchase a good-quality gear lube pump. Most pumps include adapters to accommodate different size drain holes.

You can also purchase gear lube packaged in a tube; if so, a pump is not necessary—simply insert the tip of the tube into the drain hole and squeeze the tube to inject the lube into the gearcase.

  1. Place a suitable drain pan under the gearcase.
  2. Refer to your owner’s manual for the drain and vent plug locations.
  3. Loosen and remove the drain plug. Be sure the drain plug gasket or O-ring remains on the plug. If it does not, retrieve the gasket or O-ring from the drain hole using a small pick or screwdriver.
  4. A small amount of lube will begin to drain from the gearcase. Any moisture noted dripping out is a sign that water has entered the gearcase. In this case, consult a qualified marine technician to discuss necessary repairs.
  5. Also, inspect the tip of the drain plug. Most have a small magnet attached to the tip of the plug. Fine metallic particles indicate normal wear. Larger chips or pieces of metal are a sure sign of excessive wear or breakage that will require major repair. Again, this is a good time to consult a qualified marine technician.
  6. Next, remove the vent plug. Be sure to retrieve the gasket or O-ring.
  7. Allow the gear lube to drain while noting its color and consistency. If the lube is white and milky, there is water in the gearcase.
  8. Allow the gear lube to drain completely. Screw the gear lube pump into the lube container and screw the pump hose into the drain plug hole. To prevent air pockets, always pump the gear lube into the gearcase through the drain hole. Any air inside the gearcase will exit the vent hole as the lube enters the gearcase.
  9. Continue adding gear lube until the lube begins to flow out of the vent hole. With the pump hose still attached, install a new gasket or O-ring onto the vent plug and install the plug. Tighten the plug securely.
  10. Install a new gasket or O-ring onto the drain plug. Remove the hose from the drain hole and quickly install the drain plug. Tighten the plug securely.


Inspect the propeller for chips, bent blades or other damage. After removal, inspect the propeller shaft for straightness, damaged splines, corrosion or other damage. Also carefully inspect the propeller shaft for fishing line wrapped around the shaft. Fishing line can accumulate around the shaft, damage the propeller shaft seal, and allow water to enter the gearcase.

Be careful when working around the propeller. To prevent accidental starting, place the remote control or shifter in the neutral position. Make sure the ignition key is off and remove the lanyard key from the switch.

  1. Remove the cotter pin that secures the propeller nut. Some models are equipped with a locking tab washer to secure the nut. If so, bend the locking tab away from the nut.
  2. Place a suitable block of wood between a propeller blade and anti-ventilation plate. This will prevent the propeller from turning while loosening the nut. Watch the short video below to remove the propeller and to check for fishing line wrapped around the propeller shaft.
  3. Loosen and remove the nut, washer and spacer. Slide the propeller off the propeller shaft. Remove the thrust washer located in front of the propeller if it does not slide off the shaft along with the propeller.
  4. Wipe all old grease or other material from the propeller shaft and the splines of the propeller.
  5. Coat the propeller shaft with good quality marine grease. Then slide on the thrust bearing and propeller.
  6. Install the spacer, washer, and nut. Refer to your owner’s or shop manual for the torque specification. Again, using the block of wood to secure the propeller from turning, tighten the nut the specified tightness.
  7. If the cotter pin slot in the nut and hole in the shaft is not aligned, continue tightening the nut until aligned—do not loosen the nut to align the slot and hole. Insert a NEW cotter pin through the nut and propeller shaft and bend over the ends to secure the nut.
  8. If equipped with a locking tab washer, bend the tab of a NEW washer to lock the nut in place.

Always use a good quality water-resistant marine-grade grease to lubricate the propeller shaft.

Spark Plugs

Prior to winter storage is a good opportunity to replace your spark plugs.
Refer to your owner’s manual for the recommended spark plugs and electrode gap. Carefully adjust the electrode gap using a suitable gapping tool. I prefer the wire-type feeler gauge as shown below.

Apply a small amount of oil to the spark plug threads prior to installing them. Tighten to the specification listed in your owner’s or shop manual. If a torque wrench is unavailable, turn the plugs into the cylinder head until finger tight, then an additional ¼ to ½ turn.

Power Trim and Tilt

Refer to your owner’s manual to locate the power trim and tilt pump and reservoir. Also, locate the manual release valve and tilt lock mechanism. Tilt the outboard to the full tilt position using the trim/tilt switch. Once fully up, engage the tilt lock mechanism. If necessary, you can also loosen the manual release valve and raise the motor by hand. Once fully up, tighten the manual release valve and engage the tilt lock mechanism. Use a block of wood or overhead hoist to make certain that the motor cannot fall. Do not rely solely on the tilt lock.

Inspect the trim and tilt cylinders, hoses and pump for leakage or other damage. Check the trim and tilt fluid level as described in your owner’s or shop manual. Top off as necessary using a good quality power trim and tilt fluid.


Cleaning and Inspection

Batteries generate explosive hydrogen gas, especially when charging. When working around a battery, always wear eye protection and rubber gloves. Never smoke or create any sparks around a battery.

Batteries used in marine applications are subjected to considerably more vibration and pounding than batteries designed for automotive applications. Therefore, always use a battery specifically designed for marine use.

Inspect the battery mount and hold-down device. Mount the battery securely to prevent it from turning over and spilling electrolyte. Check the electrolyte level in each cell. If necessary, fill the cells with distilled water.

Check the battery terminals for corrosion and clean as necessary. When disconnecting your battery, always disconnect the negative (-) cable first, then the positive (+) cable; likewise, to reconnect the battery, install the positive cable first, then the negative cable. This sequence is necessary to prevent creating an arc if your wrench contacts a ground while disconnecting the positive cable. Coat the battery posts and cable terminals with dielectric grease prior to reconnecting the battery.

Clean any deposits from the top of the battery using a baking soda and water solution. Do not allow any of the baking soda and water solution to enter the cells or the electrolyte will be seriously weakened. Wash off the baking soda and water solution with clean water.

Charging the Battery

Batteries generate explosive hydrogen gas, especially when charging. Therefore, always charge your battery in a well-ventilated area. Always wear eye protection and suitable gloves anytime you work around a battery. Never smoke or create any type of sparks near a battery in storage or being charged.

Check the state of charge of your battery every 30 days. The best method to check your battery’s state of charge is using a battery hydrometer. A suitable hydrometer is available from your local auto parts dealer. A hydrometer measures the density of the electrolyte as compared to pure water (specific gravity). To use the hydrometer, insert the tip into a cell, draw out the electrolyte, and take a reading on the hydrometer scale. A fully charged cell will read 1.260 specific gravity or higher. Charge the battery if any cell reads less than 1.260. Consider any cell that reads 50 points or more specific gravity less than the other cells as weak. If so, replace the battery with an equivalent marine cranking battery.

The battery’s capacity and state of charge determine the charging time required. Charging the battery at a low amperage rate helps extend the life of the battery. Attach the charger cables to the battery before switching the charger on. Be certain to connect the positive charger cable to the positive battery terminal and the negative cable to the negative terminal. Switch on the charger and check the specific gravity frequently using your hydrometer to prevent overcharging and overheating the electrolyte.

Battery Storage

It is always good practice to remove the battery from the boat for storage. In addition, the battery will lose its charge during storage. The electrolyte can freeze on an under-charged battery and destroy the battery. Store the battery in a cool, dry location to minimize the loss of charge. During storage, check its state of charge at 30-day intervals. Maintaining a full charge extends the battery’s lifespan and ensures that it will start your motor after storage.


Referring to your owner’s manual, locate each grease zerk on your motor. Give each grease zerk a couple of pumps from your grease gun containing a good quality, water-resistant marine grease. Wipe excess grease from the zerks after lubricating. Lubricate shift and throttle linkage and other pivot points under the motor cowl using white lithium based grease such as CRC 06037 Marine Grease (aerosol).


Store the outboard motor in an upright position to ensure that any water or condensation will drain from the motor. If removed from the boat, never store the motor laying on its side. Any water trapped inside the motor can freeze and cause major damage.


Question: What happens if I add too much fuel stabilizer?

Answer: Adding an excessive stabilizer can result in detonation and loss of power. However, only slightly too much will likely have no effect on the motor. Best practice is to add the recommended amount of stabilizer. Always refer to the directions on the stabilizer package.

Question: Why is ethanol (alcohol) bad for my fuel system?

Answer: Ethanol is hygroscopic. That means that the ethanol attracts water and when the two mixes it becomes corrosive. This corrosive mixture can deteriorate fuel hoses and rubber parts in your fuel system. In addition, ethanol is a powerful solvent that can dissolve sludge or other deposits in the fuel system and cause plugged fuel jets and orifices.

Question: Is synthetic oil really better for my outboard motor?

Answer: Although it is best to follow the manufacturer’s recommendation, synthetic oil can be as much as 45-50 percent better and keep sludge and contamination in suspension compared to conventional oil. Synthetic engine oil also has a lower pour point and aids in colder weather start-up. Synthetic oil is also more resistant to oxidation and chemical degradation

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