How to winterize a boat: a practical checklist and supply guide.

First, which engine setup are you storing?

Jet drive, diesel, or an unfamiliar cooling system? Get its specific manual before choosing supplies. This overview does not provide a universal drain-point map or diesel storage procedure. Boats remaining afloat also need a separate plan for seacocks, bilge pumping, and monitoring.

1. Make a plan before buying a kit

Write down the engine model, serial number, cooling-system type, battery chemistry, and storage location. Find the manual’s storage section and identify which work you can do confidently. Book the remaining jobs with a marine technician. A useful service request names each system—engine, drive, livewell, plumbing, and battery—so nothing falls between “engine winterization” and “boat storage.”

Use the manufacturer’s cooling-water supply whenever an engine must run ashore. Never run it dry, and never run a combustion engine in a garage or other enclosed area.

2. Prepare the fuel before the final run

Use fresh fuel and a storage treatment approved for your engine and fuel type. Measure the dose for the fuel aboard, then circulate it as the engine manual directs. Pouring stabilizer into the tank after the last run leaves untreated fuel farther along the system.

Tank-fill advice varies with tank design. Mercury distinguishes older vented tanks from newer sealed systems; follow your boat’s instructions and leave the required expansion space. Do not use an additive as a repair for water contamination or bad fuel. Mercury’s storage guidance is a useful starting reference.

3. Service and protect the engine

For a four-stroke, check the required engine-oil and filter service. Inspect and service the lower-unit or drive lubricant using the specified oil, fill procedure, seals, and torque. Water or abnormal debris in drained lubricant deserves investigation before storage.

Fogging is model-specific. Yamaha lists separate storage products for different applications, including an EFI storage treatment. Use your manual’s method instead of spraying aerosol fogging oil into every intake. See Yamaha’s extended-storage guidance.

4. Handle freeze protection by system

For an outboard, follow its flushing and drainage instructions and storage position. Yamaha notes that its outboards drain vertically, but blocked passages can trap water. If drainage is uncertain, have it checked. Do not assume tilting the motor up keeps it safe.

For an inboard or sterndrive, identify every required drain and raw-water component using the manual. Pink liquid at the exhaust alone does not prove protection throughout the engine: retained water and thermostat-controlled flow matter. If using antifreeze, select an engine-storage product approved for that application and climate. Permanent closed-loop coolant is a separate product and system. BoatUS explains the cooling-system differences.

List livewell and washdown pumps, hoses, freshwater plumbing, and any other water-holding equipment separately. Winterize each by its instructions. Never put automotive coolant into potable-water plumbing. Collect waste fluids for appropriate disposal rather than draining them into the yard or water.

5. Match battery storage to battery chemistry

Lead-acid batteries should go into storage charged, with their condition checked during the layup. Use a compatible charger and its recommended maintenance mode. Clean and inspect connections, and address unwanted electrical loads according to the boat’s instructions.

Lithium batteries need their own manufacturer’s storage charge level and temperature limits. Do not assume they need to stay on a trickle charger, or that a lithium charging mode makes below-freezing charging safe. Battle Born’s storage instructions, for example, describe disconnecting stored batteries rather than continuously charging them.

6. Dry the boat, support the cover, and check back

Remove wet gear, food, and portable equipment. Clean and dry compartments before covering. On a boat stored ashore, arrange drainage according to the hull’s instructions and keep outlets clear. Use a properly fitted, supported cover so water does not pool; ventilation matters too. Inspect the trailer, tires, and bearings before leaving it parked.

Storage is not a one-time check. Revisit after heavy rain, snow, or wind to look for pooling, loose straps, moisture, and drainage problems. Yamaha’s boat-storage checklist also covers drying and trailer care.

Five supplies to match to your setup.

Start with the tasks in your manual, then buy the matching supplies. The options below do different jobs; they are not competing “best kit” rankings. Check package contents, seller, compatibility, and current availability. These supplies are not universally compatible with every engine. Use the For label below each product, then confirm the exact specification in your manual.

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Before you call it finished

• Engine-specific storage steps completed and recorded.
• Fuel treated and circulated as instructed.
• Required oil, filters, gear lubricant, and seals serviced.
• Engine and every water system drained or protected by its approved procedure.
• Battery storage and charging plan matched to its chemistry.
• Compartments dry, cover supported, drainage clear, trailer checked.
• A spring note left with any removed plugs, disconnected parts, and work still needed.

Common questions

Do I need a winterizing kit for an outboard?

Not necessarily. A gravity-feed antifreeze kit may be unnecessary for an outboard that drains correctly using its prescribed procedure. Fuel care and corrosion protection still matter during a long layup.

Is “-50°F” antifreeze enough?

Read the product’s freeze and burst specifications, its intended use, and your engine’s requirements. Do not choose by the large number on the front alone. Residual water can dilute the product and reduce protection.

What if I still use the boat for winter fishing?

You need a between-trip freeze-protection plan, not a completed seasonal layup. Running the boat can reintroduce water into protected systems. Ask the manufacturer or technician which drainage steps must be repeated after each outing.

Research and sources

Prepared from manufacturer guidance and BoatUS’s winterization reference, reviewed September 30, 2026. Product selections are researched examples; Timberwake has not tested these supplies. Engine and battery manuals remain the authority for your exact equipment.

• Mercury: outboard winterization
• BoatUS: The Boater’s Guide to Winterizing
• Yamaha: boat winterizing tips
• Yamaha: extended storage and fogging products
• Battle Born: lithium battery winter storage