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How to Winterize Your Boat Before Storing It


As the boating season comes to a close, it’s time to consider how you’ll safely store your boat for the winter to avoid damage and ensure it’s ready to use in the spring. These tips will get you up to speed on how to winterize a boat, with best practices for different types of engines and systems so that your boat is protected from the elements until you’re ready to get it back into the water.

In This Article:
  1. Choose the Best Boat Storage
  2. Clean the Inside of Your Boat
  3. Flush, Drain and Winterize Plumbing Systems
  4. Winterize the Motor
  5. Treat the Fuel
  6. Winterize Your Battery
  7. Cover Your Boat

1. Choose the Best Boat Storage

You have many options for storing your boat through the off-season, including self storage, storage lots and dry docks, to name a few. The option you choose may also dictate specific steps you need to take to prepare your boat for winter storage. Consider the pros and cons of each, and choose the one that best suits your boat, location and budget.

Tip: SmartStop offers many secure, affordable options for storing boats, including indoor storage, covered storage and uncovered storage. Look for a SmartStop Self Storage location with boat storage near you.

2. Clean the Inside of Your Boat

Cleaning and prepping the inside of your boat is an important first step in winterizing. Proper care and maintenance will protect the interior — including seat cushions, wood and other materials — from mold and mildew that may develop over the winter. Here are some things to consider as you’re cleaning your boat:

  • Bag up and remove pillows, blankets, bedding, clothing and removable seat cushions, and prepare them for winter storage.
  • Remove all gear and equipment — including fishing rods, life jackets and tackle boxes — and pack them up for storage.
  • Empty out storage compartments, lockers and closets.
  • Clean out and defrost the refrigerator and freezer.
  • Spray vinyl seats and covers with mildew spray.
  • Deep clean any appliances, carpets and floors. 
  • Apply a coat of protective wax to all exposed surfaces.

3. Flush, Drain and Winterize Plumbing Systems

Any water left in the freshwater or raw water plumbing systems may freeze during the winter, causing cracked pipes and other major damage. It's important to drain all the hoses and pipes, flush them well and refill them with antifreeze. 

Tip: It's important to use the right antifreeze. You want to use food-safe propylene glycol and avoid ethylene glycol, or engine antifreeze, which is toxic. In addition, pay particular attention to the label. Avoid any antifreeze with ethyl alcohol content, which may freeze at higher temperatures than pure propylene glycol. It costs a little more, but it's a lot cheaper than repairing the damage caused by a freeze.


Here’s a step-by-step guide on winterizing your boat’s plumbing system:

  • Completely drain all holding tanks. You can do this using a water pump, or simply open all the faucets and let them flow until there is no water dripping from them. 
  • Drain the water heater, then install a bypass hose, which connects your cold water tank to the hot water faucet. After you install the hose, then fill with antifreeze.
  • Remove any water filters.
  • Close all the water taps.
  • Refill the plumbing system with propylene glycol antifreeze.

4. Winterize the Motor

No matter what type of engine your boat has, it needs special attention before the winter cold sets in. While all engines need to be drained, cleaned and refilled, the details differ significantly. Always check the documentation for your motor and follow the manufacturer's instructions on cleaning, caring for and maintaining the motor for your specific boat. The following tips are meant to be a general overview of the process.

How to Winterize an Outboard Motor

  1. Change the lower unit oil.
  2. Flush the cooling system with fresh water with the engine in the tilted-down position.
  3. For four-stroke engines, change the oil and oil filter, as well as the fuel filter and air filter.
  4. Fog the engine with fogging oil to protect it from corrosion.

How to Winterize an Inboard Motor

  1. Change the engine oil and filter while the engine is still warm. 
  2. Fill a 5-gallon bucket with propylene glycol, making sure you're using antifreeze rated for engine use.
  3. Remove the raw water intake hose from the closed seacock intake and drop it into the bucket of antifreeze.
  4. Run the engine until antifreeze is flowing from the exhaust.
  5. Fog the engine with fogging oil.

How to Winterize a Sterndrive Engine

  1. Inspect the sterndrive for cracks, damage and marine pests.
  2. Drain any water from the drive.
  3. Proceed as for an inboard motor to fill the engine with antifreeze.
  4. Drain and replace gear lube in the lower-unit drive.
  5. Check the propeller shaft for damage.
  6. Check the bilge pump operation.
  7. Check all the fluid levels. Top them off if necessary.
  8. Plug the exhaust ports to keep out pests and weather.

5. Treat the Fuel

Some manufacturers recommend draining the fuel tank before winter storage, while others suggest that the fuel tank should be full. Always follow the manufacturer's recommendations. Regardless, be sure to treat the fuel with a stabilizing additive to prevent separation, and change the water separators and fuel filters.

6. Winterize Your Battery

Your battery also needs special treatment before you tuck your boat in for the winter so you can avoid battery freeze and ensure that it will charge in the spring. You’ll want to inspect the battery for signs of corrosion or wear, and clean it or replace it if necessary. Then you’ll want to follow these steps:

  1. Charge the battery to full power.
  2. Disconnect the terminals.
  3. Remove the batteries.
  4. Store them in a cool, dry place where they won't freeze.
  5. Ideally, charge your batteries once a month, or put them on a trickle charger.
Tip: Even if you choose outdoor storage for your boat, consider storing your battery — and other boat gear — in a temperature-controlled indoor locker. When organizing your storage unit, make sure your batteries are easy to access so you can recharge them periodically during the winter months.

7. Cover Your Boat

There are many different options for covering your boat, each with their own pros and cons. Plastic covers are the most affordable option, but they're less durable and will need to be replaced after a couple of seasons. Canvas covers are more durable, but cost a bit more. Custom-fitted covers provide the best protection, but are also a more expensive option. 

Finally, many boat owners will opt to have their boats shrink-wrapped for storage. While it's the priciest option, shrink-wrapping provides the best possible seal to keep out weather, water and UV rays that can damage your boat during the off-season.

Properly winterizing your boat only takes a weekend out of your schedule, but will save you lots of time, expense and labor when it's time to recommission your watercraft in the spring. To learn more about boat storage and amenities that SmartStop offers, check out our boat storage options.

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