How To Winterize A Boat – Step By Step Guide

How To Winterize A Boat scaled

Winterizing a boat is an essential annual maintenance task for boat owners. Properly winterizing your boat will protect it from damage during the colder months and ensure it is ready to go when boating season returns. This guide will provide you with the key steps for winterizing different types of boats and engines.

Why Winterize a Boat?

Winterizing your boat is critical to prevent issues like:

  • Engine damage from frozen water expanding in the engine block or corrosion from moisture buildup. This can lead to cracks, leaks, and even engine failure.
  • Plumbing system damage from water freezing and expanding in pipes, tanks, and pumps. This can cause cracks and leaks.
  • Fuel system damage from stale fuel forming deposits and clogging fuel injectors or carburetors. This makes starting difficult.
  • Battery failure from freezing temperatures or from dying due to lack of use.
  • Mold, mildew, and rot from moisture trapped in the boat over the winter.

By taking preventative steps to winterize your boat properly, you can avoid these problems and costly repairs down the road.

Other Topics to Consider: How to keep mice out of a boat during winter storage.

Recommended Winterization Products

Fuel stabilizerAdd to fuel to prevent deposits and staleness
Fogging oilCoats engine internals to prevent corrosion
AntifreezeFor plumbing systems to prevent freezing damage
Corrosion protection sprayProtects external metal parts from elements
Battery tenderMaintains battery charge during storage

How to Winterize Different Types of Boats

The winterization process differs slightly depending on whether you have an outboard motor, inboard/sterndrive engine, or a pontoon boat. Here are the steps for each:

Outboard Motors

For winterizing an outboard motor:

  • Change lower unit oil and powerhead/engine oil. Use manufacturer recommended winter or storage oil.
  • Add fuel stabilizer to your fuel tank. Run the engine to circulate it.
  • Flush cooling system and drain water completely.
  • Fog engine by spraying fogging oil into cylinders.
  • Disconnect and remove battery. Clean, charge, and store it.
  • Clean and wash the outboard. Touch up any paint nicks or scratches. Apply corrosion protection spray.
  • Store motor in the down position securely. Do not hang it by the power cables.

Inboard and Sterndrive Engines

For inboard engines and sterndrives:

  • Change all engine fluids – oil, transmission fluid, coolant, power steering fluid.
  • Add fuel stabilizer and run engine to circulate.
  • Flush and drain the engine cooling system completely.
  • Fog the engine with fogging oil to coat internal parts.
  • Drain sea strainers and raw water pumps.
  • Disconnect and remove battery. Clean, charge, and store it.
  • Drain waste systems, ballast tanks, bilges. Add antifreeze to sinks, showers, toilet, pumps.
  • Cover engine and systems. Seal air intakes and exhaust openings.

Pontoon Boats

For pontoon boats:

  • Follow inboard/sterndrive winterization steps above.
  • Deflate pontoon tubes partially to put less strain on seams. Use pontoon plugs.
  • Flush livewell and baitwell systems. Drain completely.
  • Lubricate and protect metallic deck hardware from corrosion.
  • Remove canvas covering and store indoors. Or use vented canvas winter storage covers.
  • Elevate trailerable boats to take weight off tires. Use jack stands.

Essential Winterization Tips

Keep these tips in mind when winterizing your boat:

  • Consult your owner’s manual for model-specific winterization directions.
  • Do not run antifreeze through outboard motors. It can damage rubber seals.
  • Use ethanol fuel stabilizers to treat fuel systems if ethanol gas was used.
  • Only fog engines as needed. This step can be skipped on boats used year-round in warm climates.
  • Disconnect and remove batteries from boats in cold climates. Batteries discharge faster in cold weather.
  • Store batteries indoors in a temperature stable area if possible. Place on a trickle charger periodically.
  • Change the oil again in the spring once engines are started. Old oil from winterization use can oxidize.
  • When flushing the engine, let fresh water run for 5-10 minutes to fully clear out salt, sand, and debris.
  • Check fittings, clamps, seals for leaks or cracks during the winterization process. Replace as needed.

Winter Storage Location Comparison

OutdoorsLow costExposure to elements, need good cover
Unheated warehouseAffordable, protectedCondensation issues, batteries may still need removal
Heated warehouseOptimal conditionsMore expensive
DIY in backyardConvenientNeed space, outdoor cover

Boat Winterization Checklist


  •  Change engine oil and filter
  •  Flush engine with freshwater
  •  Drain cooling system completely
  •  Add fuel stabilizer to tank
  •  Run engine to circulate fuel stabilizer
  •  Fog engine by spraying fogging oil into cylinders
  •  Disconnect and remove battery
  •  Clean and wash engine exterior
  •  Apply corrosion protection spray
  •  Seal air intakes and exhaust openings

Fuel System

  •  Add fuel stabilizer to tank
  •  Top off fuel level
  •  Run engine to circulate treated fuel
  •  Consider adding moisture absorber to tank


  •  Drain fresh water systems
  •  Drain waste systems
  •  Add RV antifreeze to sinks, showers, pumps

Additional Systems

  •  Drain livewells, baitwells, ballast tanks
  •  Flush systems with antifreeze if possible
  •  Drain bilges completely


  •  Remove valuables and electronics
  •  Clean cabin thoroughly
  •  Open cabinets, drawers, hatches for ventilation
  •  Place moisture absorbers


  •  Wash and wax hull, deck
  •  Lubricate steering cables
  •  Lubricate deck hardware
  •  Inspect fittings, clamps, seals
  •  Apply protectants to leather, vinyl, canvas


  •  Use boat cover or shrink wrap
  •  Store indoors or outdoors protected area
  •  Use support stands or blocks
  •  Consider humidity-controlled storage


Winterizing your boat properly involves draining water from systems, treating the fuel, protecting the engine, charging the battery, and preparing the rest of the boat. While the process varies slightly across boat and engine types, addressing moisture, corrosion, and fuel degradation are key in all cases.

Consult your owner’s manual and follow these guidelines to keep your boat safe through the winter. With proper care, your boat will be ready to launch in the spring.


Do I need to winterize if I use my boat year-round?

You can skip full winterization if you use your boat regularly year-round in warm climates. However, you should still flush your motor, add fuel stabilizer, and charge your battery regularly.

What type of fogging oil should I use?

Use a marine-grade fogging oil designed for your type of engine. Some specialty fogging oils are made for 4-stroke or fuel-injected engines. Check your manual.

What should I use for antifreeze in plumbing systems?

Use a non-toxic, RV-type antifreeze. Automotive antifreeze is toxic. Use the pink propylene glycol type rather than green ethylene glycol.

Can I skip the oil change when winterizing?

No, old oil can contain moisture and acids that lead to corrosion over the winter. Always change lower unit and engine oils before winter storage.

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Steve Momot

Steve Momot

Steve is an accomplished professional photographer and marketer who specializes in the Fishing, Yacht, and Boating industry. With a strong presence as an influencer and marketing expert in the Marine Industry, he has made a significant impact in the field. Additionally, Steve is the original creator and co-founder of Sportfishtrader. Prior to his career as a marine photographer, he gained extensive experience as a licensed boat and car dealer in South Florida.

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