How to Winterize Your Boat: The Complete Checklist

Why Winterization Matters

Water expands when it freezes. If water is trapped in your engine block, water pump, raw water cooling lines, or plumbing systems when temperatures drop below 32°F, that expansion cracks metal, splits hoses, and destroys pumps. One missed step can result in a $5,000 engine repair. The entire winterization process takes a few hours and a couple hundred dollars in supplies — a bargain compared to the alternative.

When to Winterize

Winterize before the first hard freeze in your region. Don't cut it close. In the northern US, that usually means October. In the mid-Atlantic and Carolinas, November. In Florida and the Gulf, you may not need to winterize at all — check with local marinas about freeze history in your area.

Engine Winterization

Inboard and Stern Drive Engines

1. Change the engine oil and filter. Used oil contains acids that damage seals and bearings over winter. Fresh oil in = fresh engine out in spring.
2. Flush the raw water cooling system. Run fresh water through the raw water side to flush salt and debris. Use a flush adapter or muffs.
3. Fog the engine. Spray fogging oil into each carburetor/throttle body or cylinder head (for fuel-injected engines via the air intake) while the engine is running and dying. This coats cylinder walls with protective oil.
4. Drain the raw water system. Open all drain plugs in the manifolds, heat exchanger, oil cooler, and transmission cooler. Let them drain completely. On stern drives, lower the outdrive to drain.
5. Change the gear oil in the outdrive/transmission. Look for milky white oil — that means water intrusion, which will cause rust damage over winter.
6. Grease all fittings. Zerk fittings on the drive, gimbal bearing, steering components.
7. Inspect bellows (stern drives). Look for cracks, hardness, or deterioration. If in doubt, replace them now rather than dealing with a sinking boat next spring.

Outboard Engines

1. Flush with fresh water using flush muffs
2. Fog cylinders with fogging oil
3. Change lower unit gear oil
4. Inspect prop and prop shaft for fishing line
5. Grease steering tube and pivot points
6. Remove and store in upright position, or tilt fully up

Fuel System

Option A: Fill the tank completely — minimizes condensation in the tank. Add ethanol-free marine fuel stabilizer (1 oz per 10 gallons), run the engine for 10–15 minutes to distribute throughout the fuel system.

Option B: Run the tank nearly dry — then add stabilizer to the remaining fuel. Less popular but works for short storage periods.

Either way, run the engine after adding stabilizer so it reaches the carburetor/injectors and fuel pump.

Freshwater Plumbing

1. Drain the freshwater tank completely
2. Open all faucets and run until empty
3. Drain the water heater (if equipped)
4. Use compressed air to blow out all lines, OR
5. Pump non-toxic RV/marine antifreeze (pink) through the entire system
6. Flush the head with antifreeze — pump until it comes out the discharge
7. Pour antifreeze into all drain traps

Electrical System

1. Remove batteries and store in a cool, dry place (not freezing)
2. Connect to a smart battery maintainer/trickle charger over winter
3. Disconnect shore power if leaving the boat unattended
4. Apply dielectric grease to all electrical connections
5. Inspect for chafed wires, loose connections

Hull and Exterior

• Wash and wax the hull
• Apply a corrosion inhibitor to metal fittings
• Inspect and replace zinc anodes (especially if they're 50% depleted)
• Check through-hulls and sea cocks — they should operate freely
• Remove drain plugs and leave them out (prevents water from collecting and freezing in the bilge)

Canvas and Interior

• Clean and treat canvas with UV protectant and mold inhibitor
• Remove all cushions, bedding, and upholstery — store ashore in a dry location
• Clean the bilge thoroughly
• Leave locker lids propped open for ventilation
• Place moisture absorbers (DampRid or equivalent) in enclosed spaces
• Leave nothing loose that could blow around or freeze

Final Checklist Before You Walk Away

• ☐ Engine fogged
• ☐ Raw water system drained
• ☐ Gear oil changed
• ☐ Fuel stabilizer added
• ☐ Freshwater system winterized
• ☐ Head winterized with antifreeze
• ☐ Batteries removed and on maintainer
• ☐ Drain plugs removed
• ☐ Anodes inspected/replaced
• ☐ Canvas cleaned and protected
• ☐ Cushions removed
• ☐ Moisture absorbers placed
• ☐ Shore power disconnected

Winterization done right means your boat is ready to splash the moment the weather breaks. Do it once, do it thoroughly, and you'll start every season on the water instead of in the repair yard.

Get everything you need for winterization at GetBoatParts — fogging oil, antifreeze, stabilizer, and maintenance supplies in stock now.