Winterizing your boat correctly is one of the most important maintenance tasks you’ll do all year. A single freeze event can crack an engine block, split water lines, or destroy a raw water pump — repairs that can easily run $1,000 to $5,000 or more. Spending a few hours on proper winterization is cheap insurance.
This checklist covers everything from flushing the engine to protecting the hull, whether you store your boat in a heated garage, a dry-storage facility, or on a trailer in the driveway.
When to Winterize
Winterize before sustained temperatures drop below freezing in your area. In most of the northern US, this means October or November. Even if you live in a mild climate, if nighttime temperatures regularly hit 32°F, water left in your engine cooling system can freeze and cause irreversible damage.
Engine Winterization
For outboard motors: flush with fresh water for five minutes to remove salt, sand, and debris. While the engine is running, fog the cylinders by spraying fogging oil into the air intake until the engine smokes and stalls. Change the lower-unit gear oil — water intrusion shows up as milky fluid, indicating a seal failure that needs repair before spring. Remove and store the battery in a temperature-controlled space on a trickle charger.
For inboard and stern drive motors: flush the raw-water cooling circuit with fresh water, then blow it out and run non-toxic antifreeze (pink RV antifreeze, not automotive) through all cooling lines. Change the engine oil and filter — spent oil contains acids that corrode internal parts during storage. Fog the cylinders through the spark plug holes or carburetor/throttle body.
Fuel System
Either fill the tank to 95% and add a fuel stabilizer (run it through the engine for 10 minutes), or drain the tank and carburetor completely. A full tank minimizes condensation; a drained system eliminates varnish buildup from ethanol-blend fuel. For fuel-injected engines, a full tank with stabilizer is generally preferred.
Plumbing and Livewells
Drain all livewells, bilge, water tanks, and holding tanks. Open all sea cocks and drain plugs. Run antifreeze through the wash-down pump and any freshwater systems. Any water left in a non-heated environment will freeze — the expansion destroys PVC fittings, pump housings, and hose connections.
| System | Winterization Task | Notes |
|---|---|---|
| Outboard engine | Flush, fog cylinders, change gear oil | Remove battery |
| Inboard engine | Flush, run antifreeze, change oil/filter | Fog cylinders |
| Fuel system | Fill + stabilizer OR drain completely | Run stabilizer through engine |
| Livewells | Drain completely, run antifreeze | Include all plumbing |
| Electrical | Remove battery, clean terminals | Store on trickle charger |
| Hull exterior | Wax, apply corrosion inhibitor | Cover or shrink wrap |
| Interior | Clean, remove valuables, moisture absorbers | Leave hatches cracked |
Hull and Exterior
Wash the entire hull with fresh water and marine soap. Apply wax or a polymer protectant to the gelcoat to prevent oxidation over winter. Inspect the hull for stress cracks or damage that should be repaired before next season. Lift the boat or drain the bilge completely, and remove the drain plug so any rain or melt water can run out.
Covering the Boat
A quality boat cover or professional shrink wrap protects against UV damage, moisture, and debris. Shrink wrap is the gold standard for outdoor winter storage — it’s watertight, mold-resistant, and keeps pests out. A custom-fit canvas cover is reusable and works well for indoor storage. Generic tarp covers trap moisture and cause more problems than they solve.
A properly winterized boat also benefits from the right boat cover — UV-resistant, breathable covers dramatically reduce mold and corrosion during long storage periods. For spring commissioning, revisit our guide on how to anchor a boat to inspect your ground tackle and ground chain before your first outing of the season.