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How to Winterize a Boat

Oct. 7 2022 How-To By Germaine Marine

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Fall weather is starting to hit, and it’s time to start thinking about winterizing your boat. It’s best to winterize a boat before the weather turns freezing, so don’t put it off if you want to keep your boat in its best shape. Then the question is, how do you winterize a boat? If you’re not sure where to start in the winterizing process, we can help.  

Steps for Boat Winterization 

  1. Prep engine and ensure all water has been drained
  2. Apply corrosion protection
  3. Check your owner’s manual for specific instructions
  4. Add a fuel stabilizer and run the engine
  5. Change fuel filters and separators 
  6. Drain the boat’s freshwater plumbing systems, such as sinks, heads, and tanks
  7. Add antifreeze
  8. Make sure to remove water from all systems
  9. Remove drain plugs
  10. Clean and cover your boat

Winterizing Specific Systems

Now that you have the basic steps let’s go into a little more detail about how to winterize a boat. To winterize a boat well, you must keep water and moisture out as well as possible. Damage from frozen water is one of the biggest problems you can risk when you’re not winterizing a boat properly. Water in and on your boat can also cause mold, mildew, and corrosion. 

Boat winterizing calls for focusing on specific systems on your boat. We’ll look at the work your boat might need to get it ready for the cold weather. Winterizing a boat might take some time, but you’ll be glad you did it once spring rolls around again. 

Outboard Engine

When winterizing an outboard engine, the most important thing to remember is to get all the water out. Most outboard engines have a design that allows them to drain their cooling systems when you tilt them in the down position. So make sure you’re tilting the engine all the way down, and leave it like that. If you want to cover it, go ahead, but keep in mind that there needs to be ventilation, so condensation doesn’t gather, welcoming mold and mildew.

You’ll also want to protect the internal mechanisms of the engine from corrosion. The best way to do so varies. You can run fogging oil through the engine if your boat is older. If your boat is more modern, there are easier fogging processes. Sometimes, you can mix a protective product into a gas can and run it through the engine. Other times, you can winterize the outboard engine electronically. The best way to know how to winterize a boat is to check your owner’s manual.

Another way to winterize your outboard is to use it. It’s disuse that causes problems, not the cold. If you can, you can just run the engine every few weeks until it reaches average operating temps. Winter is also an excellent time to change your fluids, ensure there’s no water where it shouldn’t be, and put in fresh fluids. Boat winterizing is a good time for regular maintenance and checkups that might fall by the wayside in the warmer months.

Stern Drive

Again, the essential thing about winterizing a stern drive is to get rid of the water. With a stern drive, you have the engine block and the drive unit that will need work. You also may need to run antifreeze through the system. As with the outboard engine, the best thing to do is check your owner’s manual to ensure you’re using the best process.

You usually want to remove block plugs so water, sediment, and scale can drain from the engine. Next, thoroughly inspect exposed hoses, clamps, bellows, and other parts that might need some maintenance after a season of use. Stern drives also need fogging treatment, and it never hurts to do a quick oil change while doing all the other maintenance.

Inboard Engine

Like a stern drive, an inboard engine can be drained by removing plugs, or you can put antifreeze through the system, which might be a better option. Sometimes, inboard boats stay in the water through the winter, so you’ll have to run antifreeze through after you close the intake seacock and remove the intake hose. Then, put the end of the hose in a bucket full of antifreeze and run the boat’s engine until the antifreeze has gone through the entirety of the system.

The engine has to be at operating temperature to let the antifreeze through. It’s also best to ensure that your antifreeze is environmentally safe, so you’re not contaminating your boat's water. Inboard engines also need a fogging treatment before it’s put away for the winter, and winterizing your boat is a good time to change the oil and check for any parts that need to be replaced.

Fuel System

Every fuel system will need attention, regardless of your boat type. First, you should put a fuel-stabilizing additive to the fuel tank. Make sure you run the engine after adding the additive so the treated fuel can get into the entire system. If you don’t stabilize the fuel tank, the fuel in your tank can suffer phase separation and cause significant issues for you come spring when you start your boat up again. 

Once that critical part is done, change your fuel filters and any fuel/water separators in the system. It’s important to change the fuel/water separators rather than pour the water and reuse it. When you reuse the separator, water and sediment can get into the wrong side of the filter, which in turn can damage the internal systems. Always fully replace the filters.

Plumbing System

Boat owners often forget that the plumbing systems also need to be winterized when you’re doing the rest of your boat winterizing. If you have any kind of freshwater system on your boat, it will need to be drained completely and then have antifreeze run through it. These freshwater systems include sinks, tanks, and heads. You’ll usually have to open all the faucets until the freshwater tank is entirely empty. Once that’s done, close up the taps and put antifreeze in the tank. Again, your antifreeze should be non-toxic and environmentally safe.

After the antifreeze is in the tank, ensure all the faucets have antifreeze running through them. Antifreeze is also needed in the water heater if you have one. While winterizing the plumbing system, take the opportunity to pump out holding tanks and empty your portable MSD, if applicable. 

Winterization for In-Water Storage

Any in-water storage must also be checked. If you don’t ensure everything is taken care of, you risk mold and mildew invading your storage space. To winterize your in-water storage, close all of the seacocks and check rudder shafts and stuffing boxes. If leaks or other issues exist, tighten them or repair them as needed. Check that your battery is fully charged, clean the terminals, and add water if required.

Make sure your boat doesn’t have leaks or animal infestations and check that again regularly throughout the season. Winterizing a boat isn’t a one-and-done process. You should be checking on your boat even while it’s docked for the winter. Your bilge pumps should be working, and your float switches should activate the pumps, not blocked by debris or anything else. If your mooring area is in danger of freezing, install water agitators to bring warm water to the top. That way, your boat won’t be iced in while it’s moored.

Winterization for Out-of-Water Storage

As for your out-of-water storage, open any seacocks to allow the water to drain. This is an excellent time to pressure wash your boat's hull and remove any barnacles that live on your shafts, rudders, trim tabs, or elsewhere. Take the opportunity to wax your hull as well, if you can. While doing that, check for any blisters on the hull and get the necessary ones taken care of when you’re able. Clean your boat’s thru-hulls and filters, and ensure that your batteries are charged, and the switches are off.  

Germaine Marine Winterization Packages

Once you’ve taken care of these needs, your boat should be ready to endure the winter quite happily. However, if you don’t want to winterize your boat or are not fully sure how to winterize a boat on your own, Germaine Marine offers winterization packages to take care of your boat for the cold weather. Choose between our Platinum, Complete, and Basic Winterization packages. Now through September 30th, get 10% off on winterization services! Don’t miss out on this deal; get your boat winterized before the weather changes.

Call (801) 682-8933 or visit our website to schedule your appointment.

Platinum Winterization 

$649 + Part Cost

  • Drain engine block, manifolds, water pump, and ballast
  • Add fuel stabilizer
  • Flush and fill with antifreeze
  • Corrosion treatment to spark plugs and fuel injection system
  • Change engine oil and filter (up to 6 quarts)
  • Change:
    • Gear lube 
    • V-drive/transmission fluid
  • Grease: 
    • U-joints
    • Gimbal bearings
    • Input shaft
  • Inspect:
    • Charging system
    • Shift cable system
    • Sterndrive boots 
    • Drive shaft system
    • Trailer:
      • Tires
      • Wheel bearings


Complete Winterization 

$449 + Part Cost

  • Drain engine block, manifolds, water pump, and ballast
  • Add fuel stabilizer
  • Flush and fill with antifreeze
  • Corrosion treatment to spark plugs and fuel injection system
  • Change engine oil and filter (up to 6 quarts)
  • Change:
    • Gear lube 
    • V-drive/transmission fluid

Basic Winterization

$349 

  • Drain engine block, manifolds, water pump, and ballast
  • Add fuel stabilizer
  • Flush and fill with antifreeze
  • Corrosion treatment to spark plugs and fuel injection system

Call Germaine Marine at (801) 682-8933