Winterizing a boat: A complete guide, step by step

Winterizing a boat is an essential task to do while storing the boat before winter. And doing it wrong or not properly will affect the boat. Here are some helpful tips for winterizing the boat.

  1. Clean the boat after removing it out from the water.
  2. Stabilize the gas.
  3. Flush the outboard with fresh water.
  4. Use fogging oil (in carburetor and cylinder).
  5. Change lower unit gear oil.
  6. Remove the batteries.
  7. Cover up the boat and use anti-pest.
  8. Do regular checks during winter.

These are the basic steps for winterizing the boat. You can winterize the boat in less than 60 min. The only thing is you should be careful enough while doing that. If possible, try to keep the boat out of the water, don’t keep the boat in the water during winter.

But don’t forget about the trailer while winterizing the boat. Check my article on Winterizing the boat trailer (opens in a new tab) to winterize the trailer along with the boat properly.

A wd 40 spray is a lubricant, and it is essential for preventing corrosion over the storage period. Check the product in Amazon, click here, or click the image.

Check my article on How long you can leave the boat in the water (opens in a new tab) to know how long can you leave the boat in the water and what all precautions you need to take while leaving it in the water.

1. Clean the boat after removing it out from the water

Cleaning the boat is the major thing you need to do while winterizing the boat. After bringing back the boat from the water. Check whether there is any water in the bilge area or not, and clean it properly.

First, clean the outside portion of the boat, with any boat cleaner, and then clean inside the boat( cupboards, lockers, etc ). Once the boat is washed and cleaned properly, leave it for some time to dry. Don’t forget to clean the hull.

Boat hull maintenance is another essential thing you need to check after taking the boat out from the water. Now, we will see why do we need to maintain or check the hull after taking the boat out from the water.

Hull(underside) maintenance for a boat is essential, especially if you are boating in any saltwater. If you didn’t clean the boat hull regularly, some dirt might get stuck or algae might form and may cause any problems in the future. So, clean the boat hull regularly with the cleaner.

Some cleaning tips for a boat hull

  • Use a microfiber cloth for cleaning the boat. It is a very soft cloth and you can clean the things well with this cloth. And it will not leave any lint or dust on the surface of the boat.
  • Use any cleaning liquid. Don’t clean the boat only with water, use any cleaning liquid. If you have any tough stains on the boat, it will remove the stains easily.
  • Use a soft brush for general cleaning and a stiff bristle brush for tough stains. Don’t rub too hard with a stiff bristle brush it can peel off the paint.
  • A 50/50 mix of vinegar is a good mixture to remove any water spots in the boat.
  • Use the pressure washer(if you have any) and put some cleaner in the soap/cleaner injector place and spray it on the boat. Then wait for some time and then clean with normal water.

A pressure washer will help a lot with cleaning and washing the boat trailer and boat as well. Check the product in Amazon, click here, or click the image.

After cleaning the boat properly, drain the boat completely. And then, start the winterization process.

Check my article on 11 Simple maintenance tips for a boat: DIY (don’t worry, it will open in new tab). In that article, I mentioned all the DIY maintenance tips you can do quickly to maintain the boat properly.

2. Stabilize the gas

First, let us find, why do we need to stabilize the gas in a boat while winterizing.

If you leave the gas in the boat tank for a long, then stabilizing the gas is a must because if you didn’t stabilize the gas tank, the gas will expand in the tank, and moisture (water) will form in the tank which causes problems (corrosion) to the gas tank. So, stabilize the gas with a stabilizer.

Your other choice is to use up all of the fuel before the season’s end and put the engine away with an empty tank.

A stabilizer is essential for an outboard motor while winterizing. Check the product in Amazon, click here, or click the image.

Stabilizing the gas tank in a boat

  • There are so many brands out there. Choose the perfect one for stabilizing. Now pour the stabilizer liquid into the gas tank, don’t pour the stabilizer how much you want. For every stabilizer you buy, they will give some instructions to use.
  • Based on the instructions on the bottle, use it accordingly. If you use more, then the whole fuel (gas) will gum up. If you use less, it won’t stabilize the gas much. So, use it accordingly. They will tell to use 1oz for 10 liters or something like that, generally(quantity changes from brand to brand).
  • After pouring the stabilizer into the tank, switch on the motor and leave it for some time (like 5 – 10 min). The stabilizer will flow inside all the fuel lines, carburetors, and cylinders, stabilizing the gas.

It’s good to use the stabilizer if you are not using your boat for 2 or 3 weeks. So, you won’t get any problems in the future. If you are storing the gas for a long time, then don’t forget to use a stabilizer.

The better option would be, don’t leave any fuel in the tank. Use the gas how much you want for the day. Check this video on water formation in the gas tank, he explained it well

3. Flush the outboard motor with fresh water

First, let us find, why do we need to flush water inside the outboard motor.

While you are boating, the water will go inside and cool the motor. The water will go from the bottom part of the motor and come out from telltale. When water goes inside, it will take all the dirt particles or saltwater, which might get stuck inside. To clean that, you need to flush the motor.

You should flush the outboard motor after every use so that the outboard motor will give better performance. Suppose, if you drive the boat in saltwater and you didn’t flush the outboard motor, then it will corrode quickly.

Flushing the outboard motor

  • Generally, there will be holes at the bottom of the outboard motor, just above the propeller (and these holes may vary from the motor to motor). You need to put air muffs over there and connect it to the water pipe and start pumping the water.
  • The water will go inside the motor, and it will clean the inner walls with fresh water. After starting the process, leave it for 10 min. So, it will clean the inner walls properly. While pumping the water, don’t forget to start the outboard motor.
  • It is essential to flush the outboard motor, with freshwater, after every use. If you are using the boat in saltwater, then flush the outboard motor after every use. If you are using your boat in freshwater, then flush the outboard motor after using your boat for two or three times.

You can do this while you are starting the outboard motor after pouring the stabilizer in the tank. You can stabilize the tank, and flush the outboard motor at a time, for around 10 min. By doing that, you will save time.

4. Use fogging oil (in carburetor and cylinder)

First, let us find, why do we need to use fogging oil for an outboard motor while winterizing.

Fogging oil is used to coat the inner layers of an outboard motor with a thick layer of lubricant to prevent corrosion. If there are any water droplets in the inner layers of an outboard motor, then it will corrode and damage the motor. So, use fogging oil to prevent any corrosion inside the motor.

Fogging oil is essential for an outboard motor while winterizing. Check the product in Amazon, click here, or click the image.

Using fogging oil in an outboard motor

  • You can do this process while starting the outboard motor to stabilize the tank and flushing water in the outboard motor. The first three steps (stabilizing the gas, flushing the outboard motor with water, and using fogging oil) can be done at a time.
  • First, start with the carburetor, open the carburetor cap, and spray the fogging oil into all the carburetor holes, while the motor is running. Repeat the whole process at least, two or three times, to properly coat the inner layers of the motor.
  • While doing this process, white color smoke will come out from the outboard motor. If the outboard motor engine stops, while doing this process, it is a good sign. Which means the whole area inside the outboard motor is coated properly.
  • After completing the carburetor part, close the carburetor cap, and then open the spark plugs and start spraying the fogging oil into these holes too. So, the inner layers of the cylinder will be coated as well.
  • While doing the spark plugs part, don’t start the engine completely, just simply click the start button and stop immediately. While doing this process, just close the spark plug holes with fingers or something, for coating the inner walls of the cylinder properly.

At that time, check the color of the center electrode of the spark plugs. If the center electrode of the spark plugs is black, then change them. Generally, the white color center electrode indicates that the spark plug is in good condition

5. Change lower unit gear oil

First, let us find, why do we need to change the lower unit gear oil for an outboard motor while winterizing.

While winterizing your boat, you should change the lower unit gear oil too. If there is any water present in the gear oil, and you leave it for a long time, it may freeze and damage the whole lower unit. Replacing the lower unit of an outboard motor is a bit expensive.

Changing the lower unit gear oil for an outboard motor

  • There will be two screws fixed vertically in the lower unit of an outboard motor. It will vary from motor to motor, for some other motors there will be only one screw to change the gear oil. Remove those screws to change the gear oil.
  • First, open the lower screw, and then open the upper screw. If you open the top screw, then only all the gear oil will come out. The upper screw will hold the gear oil. If you open the upper screw first, the oil spills out. So, open the lower screw first.
  • If the gear oil coming out from those holes is thick and dark, then there is no water is present in the gear oil. If there is any change in the color of the oil and it is milky, then the oil is mixed with water.
  • When the whole oil comes out, then pump the new oil from the lower hole until you see the oil coming out from the upper hole. Then, close the upper hole with the screw, and then close the lower hole with the screw.

Don’t hesitate to change the gear oil, while winterizing your boat. Some people will not change the gear oil if there is no water content in the oil. Change the gear oil for every season, to get good performance, and to avoid any damage.

After that, spray silicon or any other spray on the wirings of the outboard motor. Just spray the silicone spray on the wiring and wherever you want. Spray it all over the outboard motor.

If there is any water stuck in the wirings, it may corrode and cause some problems. To prevent the corrosion in the wirings, use silicon spray (or any other spray). Silicone spray is water-resistant, and it will protect items from corrosion.

6. Remove the batteries off the boat

First, let us find, why do we need to remove batteries off the boat while winterizing.

Just turning off the boats outboard motor will not prevent the battery from draining. You might not be aware of it, but when your boat is turned off, your battery could still draw power from things such as the radio, bilge pump, even a clock, etc. So, remove the battery from the boat during winter.

While your boat is winterized, over time, these items will slowly drain your battery, especially if the battery is wired directly to any of these objects. You should disconnect the battery if you are winterizing your boat.

Removing the battery from the boat

  • First, clean the battery with any cleaner and get rid of any dust stuck on the battery. Then check the case properly, and make sure it doesn’t have any bulge or any other cracks on the battery. If there are any bulges or cracks on the battery means, you are overcharging the battery.
  • Next, check the terminal posts. If the terminals are corroded, then clean it up with a terminal post cleaner or any small stiff bristle brush. Next check the battery posts and clean them if they are corroded, use any cleaner or soda and clean them.
  • Every month check them and tighten them up. So, by doing that, you can prevent low voltage in the battery. If they are loose, then you will get low voltage.
  • There are two types of batteries. One is a maintenance-free battery, and another is a lead-acid battery. For both types, you need to check the distilled water level, and you need to fill it if the level is less. Use only distilled water, not any other water or tap water.
  • If you are using a lead-acid battery, then it is easy to refill the distilled water than a maintenance-free battery.
  • Then check the voltage of the batteries.
  • Finally, coat the terminal posts with grease. These are the basic steps to do every once in a season for better performance. After doing all these things remove the battery from the boat and keep it inside the home, and charge it regularly (every 2 or 3 weeks) to prevent any low voltage issues after taking it out.

Different voltage levels of all types of marine batteries are listed below in the table.

Sealed or Lead Acid
battery (in volts)
Gel battery
(in volts)
AGM battery
(in volts)

Check this boating for beginners website on removing batteries they explained very well click here (don’t worry, it will open in new tab).

7. Cover up the boat and use anti-pest

First, let us find, why do we need to cover the boat while winterizing?

Keeping the boat outdoors without any cover may damage the boat, due to the weather during winter. If the water goes inside the boat, then it won’t come out. Anything (any living creatures) can go into the boat if you didn’t cover it. So, cover the boat with any boat cover during winter.

Covering the boat

  • If you are keeping the boat indoors, then no need to worry about covering it much. But, if you are keeping the boat outdoors, then you should cover the boat with boat cover. Covering your boat will protect from elements like dirt, dust, moisture, and from any living creatures too.
  • Then remove the propeller and cover that area with some cover. Else you can keep the propeller to the boat itself if you want it to. Then cover the whole outboard motor with the cover. So, nothing can go inside the motor.
  • If you are keeping the empty gas tank in the boat, make sure that you are giving extra protection to that. If the sunlight falls on that tank directly, it may bulge, which results in changing the shape of the tank.
  • Try to remove any organic materials like canvas, leather, or other fabrics that should be removed to avoid mold and mildew. And any electronics that could freeze should be removed to avoid damage.
  • Make sure that, there are no open holes in the boat. Any small creatures can get into the boat from the holes. Then, finally, cover the boat with a strong cover. So, it can withstand any harsh weather.

Check this trailer valet website on covering the boat, where they explained all the steps to do that click here (don’t worry, it will open in new tab).

8. Do regular checks during winter

Regular checks are essential for a boat if you keeping the boat outdoors. Check the boat every one or two weeks, to ensure everything is doing well or not. Generally, in the winter, snow might fall on the boat, clean it regularly.


Winterizing the boat for winter is essential. If you didn’t do that, you will end up with problems in the boat. And make sure that you will do the right way.

Mix 30% vinegar with water and spray it on the boat. What it does is it will remove the water strains, if there are any on the boat. After spraying the vinegar, just rub it with the cloth. So your boat will look clean, and it will look like it is polished.

Winterizing both the outboard motor and inboard motor is the same. The only difference is for an outboard, we can remove the motor out. Whereas for an inboard, we can’t remove the motor out.

Check this video on winterizing the boat, where he explained it very well. I know it is a lengthy video, but it is very helpful.

Related questions

1. What happens if we didn’t winterize the boat during winter?

If you didn’t winterize the boat, suppose if there are any water or water droplets left in the outboard motor, it will corrode. And if there is any water in the lower unit gear oil, it will damage the lower unit of the motor. You can use your boat peacefully if you winterize your boat in winter.

2. Is winterizing a boat is difficult?

Winterizing a boat will be difficult, if you re doing it for the first time, all you need to do is to practice it on your own. It is easy to make mistakes while winterizing a boat. After doing it 2 / 3 times, you can winterize the boat in less than an hour. There are only a few steps to follow.


My name is Mahidhar, and I am passionate about boating. Every day I learn some new things about boats and share them here on the site.

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