Unless you live in a warm climate and use your boat year-round, “winterizing” is important to protect your investment and ensure that is ready to go next season.  In this article, we’ve developed a boat winterization checklist based on our recent survey of 155 boat owners in the US.


If you live in a cold climate with temperatures below freezing, properly winterizing your boat will prevent any residual water in your engine block, drive shaft or gear case from freezing and expanding and severely damaging your engine.  However, even those who live in more moderate climates should “winterize” if they don’t plan on using their boats for an extended period of time (few weeks or more).  This is because inactivity can also be harmful to engines because of corrosion and fuel degradation.


The answer to this question may  seem obvious to those living in colder regions.  You clearly want to winterize your boat before experiencing freezing temperatures in your area.  October is the most popular time to winterize; nearly half of boaters in our survey (48%) winterize at this time.  However, for those who live further south where the coldest temperatures are around 20 or above, November is also a common time to winterize.

The question gets a bit more complicated if you own an inboard or sterndrive powered boat and wish to extend your season as long as possible.  Unlike outboards, these engine types hold water in the engine block that must be drained or treated (with antifreeze) to prevent freezing and cracking the block.  But, once you do this, you are basically done for the year – even though you might experience many nice days after an early cold snap.

However, one alternative is to add a block heater.  Here is a unit that I have used before that isn’t too expensive and gets good reviews on Amazon: Caframo Pali Engine Compartment Heater.  This electric heater is thermostat controlled and will kick on when temperatures drop below 42 degrees.  It is also designed to be ignition safe for use in bilge compartments.  Of course, this solution requires access to electricity and you still need to be sure that your lower unit and gear case are drained as well (more about this later).


The following are the most frequent winterization activities performed by boat owners along with a brief description for why it is important to do each.

  1. Clean Your Boat  It is important to clean your boat inside and out to prevent stains or marine growth from setting in and making it much more difficult to treat later.  Nearly 8 in 10 (79%) boaters in our survey clean their boat at the end of the season.  See our previous article on “Best Boat Cleaning Products: Unbiased Review” for suggestions and a review of cleaning products for various surfaces.
  2. Wax Your Boat  After cleaning your boat, it is also a good time to wax it.  And, if you store your boat outside (33% keep their boat in their yard or in an outdoors commercial lot), it is especially important since UV Rays will cause fading and oxidation (fiberglass).  One-third (33%) of boaters who winterize their boat perform this step.  A good marine wax made with Carnauba such as Collinite will give you the best shine.  However, a polymer (e.g., Starbrite Marine Polish) will bond better and last longer.  See “Best Boat Wax: Unbiased Review” for additional details.
  3. Remove Electronics and Stowed Items  Items like Fish Finders, VHF Radios, life jackets, water toys and even removable cushions should ideally be removed before storing your boat for an extended period of time.  The most obvious reason is theft prevention.  Additionally, mildew, condensation and corrosion could form if the area is not well ventilated.  LCD screens (the “L” stands for liquid) could also be damaged if exposed to extreme cold (say, below -20 F).
  4. Top Off the Fuel Tank  There used to be a debate as to whether to empty the tank or fill it up.  Now, the matter is largely settled as most advocate filling her up.  The reason?  Filling the tank does not leave room for condensation which is the cause of most problems.  Nearly half (47%) of boaters in our survey top off their tank.   Only 19% did the opposite and emptied it.
  5. Add Fuel Stabilizer  Adding fuel stabilizer helps keep your fuel from degrading over the long winter months.  Nearly 8 in 10 (78%) of boaters in our survey indicated that they do this as part of their winterization procedures. Also, you will want a product that treats ethanol if there is the possibility that you have this in your fuel. This is to deter “phase separation” when water separates from the fuel and settles to the bottom of your tank which can be extremely harmful to your engine. There are several quality products available to choose from that both stabilize and treat ethanol. One such product is Sta-Bil which is very popular and something that I add each time I fuel my boats throughout the year.
  6. Flush the engine with fresh water  If you are a saltwater boater, this is a standard procedure whenever you use your boat.  But freshwater boaters should minimally do it too at the end of the season to remove any dirt or debris that might have collected.  One-third (33%) of boaters in our survey indicated that they flush their engine with fresh water when winterizing their boat.
  7. Change the lower unit gear lube  For most engines, it is recommended that you change your gear lube about every 100 hours or at least once a year.  Doing it at the end of the season has the added benefit of ensuring there isn’t any moisture in the gear case that could cause problems in freezing temperatures.  In our survey, 6 in 10 boaters (62%) change their gear lube before putting it away for the winter.  If your old gear lube appears white or creamy when changing it, you should take it to a dealer to have it inspected for possible leaks/broken seals.  And, when storing your boat, it is important to tilt the engine all the way down (vertical) to drain any water from the lower unit.  Otherwise, water could collect and freeze which might bust your gear case.
  8. Change engine Oil and Filter (and fuel filter)  If you have a sterndrive, inboard or four-stroke outboard engine, it is recommended that you change your oil and filter approximately every 100 hours (manufacturer recommendations may differ).  And, it is a good practice to do this at the end of the boating season.  According to BoatUS, “residual acids and moisture left in the crankcase over the winter can pit bearings and other vital engine parts.”  Fifty-eight percent of boaters in our survey change their engine oil and filter as part of their winterization procedure. While you are at it, this is also a good time to change your water-separating fuel filter – especially considering the problems that can occur with ethanol as noted earlier.
  9. Fog Engine  Fogging the engine provides a protective coating that inhibits corrosion to the cylinders and internal components.  It involves spraying “fogging oil” into the carburetor or air intake until smoke is emitted.  It is best to also remove each spark plug and spray some additional fogging oil into each cylinder for good measure.  Nearly half (47%) of those who winterize their boat fog their engine.
  10. Charge (and ideally) remove the batteries  Before putting your boat away for an extended period, it is important to check that your batteries are fully charged.  This is because batteries naturally discharge over time.  According to BoatUs, a typical lead-cell battery will lose approximately 5% of its charge per month.  And, boaters in our survey indicated that they store their boats for approximately 6 months during the off season.  This adds up to about a 30% discharge which could impact the life and performance of your battery. Unless your boat is kept on the water (and so you may need the battery to operate your bilge pump), it is best to remove your battery from your boat and periodically “top it off” to keep it from running down too much during the off season.

Additional Step for Sterndrive and Inboard Owners

Because Sterndrive and Inboard engines retain water in the engine block, your boat winterization checklist should also include one or both of the following steps if your boat might be exposed to freezing conditions.

  • Drain the Engine Block  This involves removing the drain plugs on the lower portion of the block to let the water drain into the bilge (and you need to take out the boat plug to drain that water from your boat).  Unfortunately, the plugs are often difficult to reach and so you might need to take your boat to a marine mechanic to do this.  However, there is a little known but very handy feature on “newish” MerCruiser models that make this process much easier.  There is a blue knob that you turn to open and close Boat Winterization Checklist - the MerCruiser Season Extended Featurethe drain plugs.  Turning it clockwise closes the plugs for normal engine usage.   Counter-clockwise opens the plugs and drains the water from the engine block into the bilge.  With this “season extender” feature, you can easily drain the water if you anticipate freezing temperatures and then close the plugs when you are ready to get back out on the water (just be sure to stow your drive in the down position so that drains too).   I have a 2013 MerCruiser 5.0L engine and the knob is located in the upper right corner of the engine (when viewed from inside the boat).
  • Add anti-freeze  For those who want to be extra cautious, you can add a water/antifreeze solution after draining the block (and closing the plugs).  You will need to run your engine to do this and there are several YouTube videos available to show you how it’s done.  This extra step ensures that there is no residual water to potentially freeze or cause corrosion.  However, it is important to note that the antifreeze used for boats (environmentally safe) is very different from that used for automobiles (highly toxic) so be sure to use one specifically made for marine applications.

Extra Credit

These boat winterization checklist items are not mandatory for cold weather but are good things to minimally check at the end of the boating season:

  • Grease the prop shaft  Another simple but helpful step is to grease your prop shaft.  This will prevent rust from forming and “freezing” your prop to the shaft.  Simply remove your prop and apply a liberal amount of marine grease (such as Mercury 2-4-C or Yamalube Marine Grease) before replacing it.
  • Grease trailer bearings  If you trailer your boat, it is important to inspect your bearings periodically to reduce the chances of failure on the road.  Trailer manufacturers generally recommend replacing the grease every 3,000 or 4,000 miles or once a year.  However, if you have Bearing Buddies, you should not have to maintain them as often. Nearly 1 in 4 boaters (22%) inspect/grease the trailer bearings as part of their winterization process.  However, those who do all of their maintenance themselves are more likely to do it (35%).

If you follow the above boat winterization checklist, your boat will be well protected over the winter months and ready to go next spring.  Most are simple to do and don’t require extensive mechanical skills.  In fact, nearly half of boaters who winterize their boats (47%) do all the work themselves.  Outboards are especially easy to maintain which is part of the reason why they have grown in popularity in recent years.

If you have other winterization tips and suggestions, please share them in the comments section below.

Special thanks to the many boat owners who took the time to share their input in our winterization survey and for helping to build one of the most trusted resources for boaters on the internet.  If you would like to receive our free monthly newsletter with our latest reviews and studies, click on the “register” button at the top of the page.


Jerry Mona, BoaterInput, survey of 155 boat owners in the US in fall/winter of 2019 (this is where the above survey findings originated).

Changing Oil in Your Boat, BoatUS, July 2012.  (this article mentions why you should change your engine oil at the end of the season or before storing the boat for a prolonged period)

Frequently Asked Questions – Oils and Lubricants, Mercury Marine. (in this Q&A section, Mercury discusses why it is best to change your oil and gear lube at the end of the season)

What You Should Know About Boating in Freezing Weather, Mercury.com, November 19, 2019 (Discusses why you should always store your engine in the down position during freezing weather)

Bob McNally, Tips to avoid annoying boat and motor troubles, Jacksonville.com (Florida Times-Union), August 4, 2012. (Discusses why it is important to store engines (especially 4-strokes) vertically – even when not freezing)

Tom Burden, Busting Ethanol Fuel Myths, WestMarine.com, June 1, 2020.  (This article talks about the problems with ethanol-blended fuel and what you should do about it)

How Cold Weather Affects Electronics, Global Electronic Services, Inc. (Briefly discusses why cold weather is harmful to batteries and LCDs)

 A Few Tips for Winterizing Your Marine Electronics, Garmin.com, August 22, 2013.

Megan Molteni,”Why Your Phone (and Other Gadgets) Fail You When It’s Cold“, Wired.com, January 30, 2019.

Charles Plueddeman, The Outboard Expert: Propeller Shaft Care Essentials, August 17, 2007 (Why it is important to grease your prop shaft occasionally)

John Tiger, Maintaining Boat Trailer Wheel Bearings, BoatingMag.com, February 25, 2020 (Describes how to grease your trailer bearings)

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