How to Winterize Your Boat Properly

Proper winterization protects your boat investment from freeze damage, corrosion, and deterioration during months of storage. Taking time to prepare systems correctly prevents expensive spring repairs and ensures your vessel emerges from winter ready for another season.

Quick Answer: Complete winterization includes draining or treating all water systems, fogging engines, changing fluids, protecting fuel with stabilizer, and covering or storing the boat properly. Professional winterization typically costs $300-800 depending on boat size and systems.

Engine Winterization

Outboard Engines

Flushing with fresh water removes salt and debris from cooling passages. Run the engine on a flush attachment until it reaches operating temperature, allowing the thermostat to open and circulate water throughout the system.

Drain the lower unit completely by removing both the top vent plug and bottom drain plug. Water trapped in the gear case expands when frozen, cracking housings and destroying gears. After draining, refill with fresh gear oil to protect bearings through storage.

Fog the engine by spraying fogging oil into the carburetor or air intake while the engine runs. This coating protects cylinder walls and internal components from corrosion during storage. Alternatively, remove spark plugs and spray fogging oil directly into each cylinder.

Stabilize fuel in the tank and run the engine long enough for treated fuel to reach the carburetor or injection system. Untreated gasoline degrades within weeks, forming varnish that clogs fuel system components.

Inboard Engines

Raw water-cooled engines require complete draining of all cooling passages, hoses, and heat exchangers. Open all drain petcocks and remove hoses from low points to ensure no water remains. Even small amounts of trapped water can freeze and crack expensive components.

Closed cooling systems need antifreeze protection appropriate for expected temperatures. Check coolant concentration with a hydrometer or refractometer, adjusting as necessary for your climate.

Change engine oil and filters before storage. Used oil contains acids and contaminants that promote corrosion during idle periods. Fresh oil provides better protection through winter months.

Fog cylinders using the same procedures as outboard engines. Diesel engines benefit from changing fuel filters and treating fuel with biocide to prevent algae growth.

Stern Drive Systems

Stern drives require special attention at the universal joints, gimbal bearing, and bellows. Inspect rubber components for cracking or deterioration, replacing as needed before storage. Grease all fittings according to manufacturer specifications.

Drain the drive unit completely and refill with fresh gear oil. Check the outdrive oil for water contamination, which appears as a milky color. Water in the gear case indicates seal problems requiring immediate attention.

Fuel System Preparation

Treating Fuel

Add fuel stabilizer to the tank before the final fall run. Follow dosage recommendations carefully, typically one ounce per gallon. Run the engine to circulate treated fuel throughout lines, filters, and injectors.

Fill tanks to 90-95% capacity to minimize condensation while leaving room for expansion. Empty tanks accumulate moisture that promotes corrosion and fuel contamination.

Ethanol Considerations

Modern E10 gasoline presents special winterization challenges. Ethanol attracts water and can separate from gasoline during extended storage, potentially damaging fuel systems. Consider using non-ethanol fuel for winter storage when available, or add ethanol-specific fuel treatment products.

Fresh Water System Winterization

Complete Drainage

Open all faucets and drain valves, including the water heater. Run the fresh water pump until pressure drops, then open the pressure switch access to drain remaining water from the pump housing.

Remove inline water filters and drain completely. Frozen filters crack easily and are expensive to replace.

Antifreeze Protection

Use only non-toxic propylene glycol antifreeze rated for potable water systems. Never use automotive antifreeze, which is poisonous and will contaminate water systems requiring extensive flushing to remove.

Pump pink antifreeze through all lines until it appears at each faucet. Don’t forget heads, showers, and any other fixtures connected to the water system.

Sanitation System Winterization

Holding Tanks

Pump out holding tanks completely before storage. Add holding tank treatment products according to directions, then add non-toxic antifreeze to protect against freezing.

Marine Heads

Pump heads dry, then add pink antifreeze to the bowl. Operate the pump to distribute antifreeze through valves and hoses. For manual heads, work the handle to coat internal components with antifreeze.

Battery and Electrical Systems

Battery Storage

Disconnect batteries to prevent parasitic drain from electronics and switches. Clean terminals with baking soda solution and apply corrosion-preventive grease.

Store batteries in a cool, dry location and maintain charge with a quality battery tender. Fully charged batteries resist freezing, while discharged batteries can freeze at relatively mild temperatures and suffer permanent damage.

Electronics

Remove portable electronics to climate-controlled storage. Fixed electronics benefit from heaters or dehumidifiers in covered boats to prevent moisture damage.

Hull and Cover Protection

Canvas and Covers

Quality covers prevent snow, ice, and debris accumulation while allowing air circulation. Poorly designed covers trap moisture, promoting mold and mildew growth that damages upholstery and headliners.

Support covers with frame systems to prevent water pooling. Check covers regularly through winter, clearing snow loads and adjusting as needed.

Shrink Wrapping

Professional shrink wrap provides excellent protection for boats stored outdoors. Include vents for air circulation and access doors for periodic inspections. Quality shrink wrap application typically costs $12-20 per linear foot.

Spring Commissioning Preview

Proper winterization makes spring commissioning straightforward. Document all winterization steps so you or your yard can efficiently reverse the process when boating season returns. Photograph drain plug locations and record any issues discovered during preparation.