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How to Winterize an Outboard Boat Motor in 5 Simple Steps

Fact checked by William Hart

how to winterize an outboard boat motor

As the weather starts to cool down, boaters need to prepare their vessels for winterization. An outboard winterization aims to cleanse the entire engine system and add additives so the harsh winter won’t freeze the engine and the liquids inside it.

Below, you will find a five-step guide on how to winterize an outboard boat motor that you can follow along. Whether you’re dealing with a 4 or 2-stroke outboard boat motor, we’ve got you covered.

Table of Contents

What to Prepare


The products you need include:

  • Fuel stabilizer
  • Fogging oil
  • Gear lube oil and pump
  • Outboard motor oil (for 4-stroke outboard motor only)
  • One gallon of antifreeze
  • Marine grease

The tools you need include:

5 Steps to Winterize an Outboard Motor


Step 1. Treat the fuel with a fuel stabilizer

The first step to winterizing an outboard motor is to treat the fuel. Follow the manufacturer’s instructions to know much stabilizer you should use and pour the needed amount into your gas tank. The stabilizer keeps your gas from freezing and forming buildup during the upcoming storage time.

After adding the additive, you should run the engine so the stabilized fuel can travel through the entire system. Follow these steps:

  • Attach the flush muffs to a garden hose
  • Place the muffs onto the engine water intake hole
  • Turn on the water supply
  • Start the engine and leave it on for at least five minutes

Note: Make sure water flows to the engine before you turn it on. Starting your engine dry will cause irreversible damage.

Step 2. Replace the crankcase’s oil and filter (For 4-stroke motor only)


To drain out the old oil in the crankcase, you should:

  • Remove the cowl of the engine compartment
  • Find the oil sump drain plug below the crankcase
  • Place a container underneath to catch the oil as it drains out
  • Remove the sump drain plug

After draining the oil, you will need to replace the oil filter.

  • Remove the old crankcase oil filter (You might need a filter wrench or adjustable strap wrench)
  • Lightly coat the O-ring on the new filter with outboard motor oil
  • Carefully screw the new filter in place

Some Yamaha outboard motor models, such as F8 and F9, don’t come with an oil filter. Instead, they have an oil strainer in the crankcase. You need to replace this strainer at least once a year. Follow the owner’s manual for the specific procedure.

When the system is nice and clean, you can add new oil.

  • Find the oil plug on the back of the powerhead and remove it
  • Fill new oil into your crankcase using a funnel (Pay attention to adding the correct amount)
  • Reinstall the oil plug
  • Turn on the water supply and run the motor for five to ten minutes
  • Pull the oil dipstick out and check the oil level

Step 3. Change the lower unit oil and filter

Regardless of when you last changed the lower unit oil, you need to do it again. Water can get into the lower unit when the boat is in use. If you store it like that, the water will freeze and damage the system.

Follow this procedure to drain out the old oil:

  • Find the drain plug at the bottom of the lower unit and the vent plug above it
  • Place a catch pan underneath the drain plug
  • Remove the drain plug with a screwdriver
  • Remove the vent plug (Remember to take off any gaskets that come with it)

You will see oil flowing out of the bottom drain hole. The gear oil should look translucent with a hint of green. If it has a milky color, water has penetrated your gearbox. It happens because one of the metal gaskets broke or corroded.

In that case, you must inspect all of the gaskets and plugs for signs of damage. Then, replace them. When fixing the leaks, pump new oil into the lower unit.

  • Screw the oil fitting to the drain plug hole
  • Place the nozzle of the gear lube pump into the unit
  • Screw the pump into the oil bottle
  • Pump until oil flows out of the vent hole
  • Quickly reinstall the vent plug
  • Remove the pump and reinstall the drain plug

In addition, grease will gather on the oil filter and cause clogs over time. This reduces the volume of oil running through your engine. So, you need to change the oil filter periodically. Since each brand has a distinct procedure, you should refer to your owner’s manual.

Step 4. Add fogging oil to the cylinders and flush the engine with antifreeze


Fogging oil will keep rust from forming in the cylinders, while antifreeze will prevent the remaining water droplets from freezing and damaging the system. You can do both in one procedure.

  • Run the engine for at least five minutes to warm it up
  • Disconnect the garden hose and the flush muffs
  • Fill the winterizing kit with antifreeze and connect it to the flush muffs
  • Remove the cowling of the air intakes
  • Open the winterizing kit’s valve
  • Restart the motor to run antifreeze through the system

While the engine is running, spray the fogging oil into the carburetors. Keep spraying until the engine emits white smoke. After that, disconnect the fuel line from the engine and continue spraying the oil into the engine until it shuts down. Doing so will help the engine consume all of the fuel in the carburetors.

For an electronic fuel ignition (EFI) motor, you can’t run the fogging oil to the carburetors. Instead, you will make a mixture of gasoline, two-cycle engine oil, and a fuel stabilizer in a container. Then, use a fuel line to run this mixture through the fuel system.

Step 5. Grease the tilt tube and pivot tube

Many boaters find their tilt tube and pivot tube stuck when they launch their boats in the spring. To prevent that, always grease the tubes before storing them.

Load your grease gun with marine grease, locate the zerk fittings for the tubes, and squeeze a generous amount of grease into the fittings. Finally, inspect the engine and propeller for any damage, and replace the cowl.

Winterizing a boat’s outboard motor properly requires time and experience. This video will walk you through the whole process:


It’s hard to believe that the boating season has ended, but it’s time to prepare your motor for winterization. Learning how to winterize an outboard boat motor and doing it yourself will keep you from the service cost of winterizing your outboard motor every winter.

As a last reminder, always store your engine in an upright position so that liquids inside it stay in the correct compartments. If you have any questions, send us a message via the contact page. We’ll soon respond. Thank you!

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