How to Winterize a Boat

What goes into winterizing a boat or marine equipment varies greatly depending on where you are in the country. Generally speaking though, anyone who lives in an area that will see a temperature consistently below the freezing point, or areas that potentially can hold a temperature below 32 degrees for several days, should properly winterize their boat to protect the engine and other components. The first step to winterizing a boat is to identify the type of boat you have, and whether your boat will remain in-water (in a marina) or out of water, like most boats. The main difference in boat designs is going to be engine related – does the boat have an inboard engine or outboard? If the boat is an inboard engine, is it a true inboard, or inboard/outboard with a stern-drive on the back? Each type of boat will handle winterization slightly differently, but the overall concept is very similar. When breaking down the winterization process, the best method is to break it down into each key area – Fuel and intake, Cooling, output drive, septic (if applicable), and outdoor protection. To properly winterize your boat, you are going to need the following items and supplies:

  • Sta-bil fuel stabilizer
  • RV antifreeze (3-5 gallons)
  • Fogging Oil
  • Marine Hose Flush tool or “earmuffs”
  • Large Bucket
  • Submersible pump (small sump-style pump works best)
  • Garden Hose

How to Winterize a Boat

1. Protect the Fuel

Fuel (either gas or diesel) breaks down over time, and the 3-5 months that your boat is going to be sitting can change the complexion of the fuel not only within the tank, but the lines and carburetor / fuel delivery. Start by adding the appropriate amount of Sta-bil fuel stabilizer to the tank. Hook up your garden hose to a direct water supply and connect to your earmuffs on the water intake of the stern-drive or outboard motor. Start the engine. Your first goal is to run the engine for several minutes, allowing the fuel with Sta-bil to enter the fuel system completely. After several minutes, shut the engine down.

2. Protect from Freezing

The next step differs slightly depending on the type of motor you have – either Outboard, Inboard, or Inboard/Outboard, commonly referred to as a “stern drive” or “I/O”. Most outboard motors will naturally drain their internal water once the boat is removed from the water and allowed to hang completely down. If there is any doubt though that residual water could still be in the motor, you can resort to the next step that inboard/outboard motors must do – drain the water and/or fill the system with RV antifreeze. If your boat is a true inboard motor (not an inboard/outboard or stern-drive) then the chances are your boat has a contained cooling system similar to an automobile that uses actual auto antifreeze and a radiator. If this is the case, no winterization is needed other than to check the antifreeze’s freeze-resistance with a hydrometer, to make sure it’s prepared for cold winter. If your inboard motor uses raw lake water to cool like an inboard/outboard motor does, then the system will need to be drained of all water and/or filled with RV antifreeze. On these engines, remove the block drain plugs or lower radiator hose to drain all water in the block. If you wish, you can stop here, but generally it’s a good practice to fill the motor with RV antifreeze as well as some water will remain in the block. Some people prefer to not drain the block and simply replace the water with RV antifreeze by allowing the motor to take in RV Antifreeze. If you have an outboard you chose to fill, or an inboard/outboard, the next step is to fill your bucket with RV antifreeze. Place your submersible pump in the bucket, with the garden hose hooked to your earmuffs and to the water intake. The goal here is to plug the pump in, fire up the motor, and begin circulating RV antifreeze into the engine and system. Regardless of whether you initially drained the motor of water or kept the water in it, you will start to see water drain out the exhaust of the drive (this is where hot water exits, usually around the center of the prop) as the engine is filled with RV antifreeze. Be sure to watch the level in the bucket carefully. Some systems take nearly 6-8 gallons before clear water stops running out and the system is filled with antifreeze. Outboard motors will take very little – generally only about a gallon. Most of this in an outboard will drain out once you shut the motor off. Finally, make sure that the engine sump and/or bilge area of the boat is completely drained. Usually this is a plug in the back of the boat that you remove at the boat launch. Just be sure you removed it the last time you were out! Make sure you put it somewhere where you will easily find it! It is important to understand that protecting your engine from freezing is without a doubt the most vital part of winterization. Frozen water in an engine will at best pop out a freeze plug. At worst, it will completely crack the engine block, which is not uncommon. Many owners will simply drain the water from the block, but understand these drains often do not completely drain the system. Filling the system with RV antifreeze is the only way to protect the entire system.

3. Fog the Intake

Fogging oil is a thin, protective oil in the form of a spray-can. It is meant to spray out as a dense mist, or “fog” and be sprayed directly in the intake of the engine. The purpose is to coat the cylinder walls and valves with oil, and protect them from the winter months – especially the springtime when melting snow and rapid temperature changes can create super-humid and cold conditions in the air that lead to rust. Engines don’t like to run on fogging oil, and they won’t run long, but you have to be sure to allow the motor to ingest enough fogging oil to completely coat everything. To do so, follow the next steps.

On an inboard motor, remove the air cleaner so you have direct access to the carburetor or throttle body. On an outboard motor, you will need to remove the engine cover and locate the intake. The best time to achieve fogging is when you are about to shut down the motor after ingesting RV antifreeze (step 2). The idea is that you are going to fog the motor for approx. 10-15 seconds, then shut the motor down by over-fogging. First, begin fogging with short bursts about 1-1.5 seconds and let the motor recover. You will notice that when you spray, the motor will stumble and spit out white smoke (this is burned fogging oil). Do this several times over about 10 seconds, then spray a constant spray for the final dose. The motor will stumble, and in most cases, will then die. If the motor doesn’t die after 4-5 seconds of spraying, have someone shut the motor off as you are spraying. At this point, fogging the engine is complete. This will now offer the winter protection internally you need.

4. Address the Drive Oil

Drive oil, or output gear oil lives a tough life. It works the same as differential gear oil in a car, only its entire life is spent inside a case that is underwater. In most cases, even the best of motors and drives leak a little bit of water. Because of this, it is highly recommended that gear oil is changed out every season. The best time to do this is in the fall, so that any water in the system is eliminated and not given several months to sit, separate into water and oil, and contaminate the system. Start by removing the plug and draining the drive oil completely. A good idea is to leave the drive to drain for 30 minutes to an hour while you do something else. This ensures everything is completely drained. Next, fill the system up with fresh oil for the winter and next season. You can also choose to do an engine oil change at this time.

5. Septic and Water Systems

Septic systems on boats are generally only for boats larger than 22′. These can be small toilets, showers, or any contained water system. Any standing water in the boat needs to be properly drained. Toilets can be filled with a small amount of RV antifreeze to ensure anything inside is protected from freezing. Keep in mind that even a boat being stored in water in a marina may face temperatures cold enough to burst a water pipe, even though the lake may not freeze.

6. Outdoor Protection

Many boat owners simply don’t have the space to store their boat indoors. Because of this, extra protection is needed over the winter to make sure your boat stays safe, especially in northern areas with a lot of snow. First, be sure your boat cover is sturdy and will hold the weight of extra snow. Check its tear resistance as it gets older by trying to stretch it gently over the edge of the boat. If it rips, the chances are, it would rip under the weight of snow. Make sure your cover has enough internal support to hold up snow and not have it crash down into the boat. This can be accomplished with 2×4’s across the bow and stern of the boat, and even sheets of plywood cut to allow the cover to rest on top and take the weight of any snow. Any time it snows, it’s a good practice to get the snow off the cover as soon as possible. Next, protect the interior from rodents who can easily seek shelter with rodent repellants and traps. Nothing is worse than having a great winterization only to find out you have to clean out multiple rodent nests that formed over winter. Remove any batteries in the boat and bring them indoors or into the garage. You can choose to hook them up to a trickle charger once indoors, but just getting them out of the elements will ensure a longer life.

Jet Drive Boats / Personal Watercraft

Jet Drive watercraft generally has less winterization as there is no drive component oil to change, and most water will drain from the craft when it’s removed from the water. Starting the craft out of water for a quick 5-10 seconds and turning the wheel from side to side will expel any last bit of water in the system, but do not run the engine for longer than 5-10 seconds. All other points of winterization – Fuel Stabilization and Fogging apply the same to these crafts.

If you follow these winterization steps, your chances of winter damage to your boat are massively reduced, putting you back on the water easily come next summer!

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