How to Winterize Your Boat: A Step-by-Step Checklist

Winterizing is the cheapest insurance a boat owner can buy. Water left in an engine can freeze and crack a block, old fuel can gum up a fuel system, and a damp, sealed hull grows mildew by spring. An afternoon of work in the fall saves you from a repair bill when the season opens. This checklist walks through the main steps and the gear for each one.

Always check your engine and boat manufacturer's manual first. Procedures differ between outboards, sterndrives and inboards, and the manual comes first when it disagrees with this guide. If you're unsure about any step, ask your marina or a marine mechanic.

Step 1: Stabilize the Fuel

Gasoline starts to break down within a few weeks, and ethanol blends can absorb moisture. Add a fuel stabilizer to the tank, then run the engine for several minutes so the treated fuel reaches the whole fuel system.

• Fill the tank (about 90%) to leave less room for condensation
• Add stabilizer at the dose printed on the bottle, based on your tank size
• Run the engine to circulate it

Gear: Fuel stabilizers and treatments: STA-BIL and Star brite formulas for gas and diesel.

Step 2: Flush and Protect the Engine

Flush the cooling system with fresh water to remove salt, sand and debris before storage. Then protect the internals:

• Flush kit or muffs: connect to the water intake and run fresh water through the engine
• Fogging oil: spray into the carburetor or cylinders as directed to coat internal parts against rust and corrosion

Gear: Engine flush kits and fogging oil.

Step 3: Drain Water and Clean the Bilge

Any water left in lines, livewells, bilge or washdown systems can freeze and expand.

• Drain the livewell, bilge, fresh water tanks and washdown lines per your manual
• Clean the bilge with a bilge cleaner and let it dry
• Leave drain plugs out and store them somewhere you'll remember

Gear: Bilge cleaners available in our Winterization collection.

Step 4: Control Moisture and Protect Batteries

A closed-up boat traps humidity, which leads to mildew and musty cushions.

• Place moisture absorbers or dehumidifier bags in the cabin and storage compartments
• Open cushions and lockers to let air circulate
• Remove batteries or keep them on a maintainer, stored charged in a cool, dry place

Gear: Moisture absorber bags and heater blankets, found in the Winterization collection.

Step 5: Cover It Properly

A good cover keeps off rain, snow, UV and debris. A cover that traps water or sags does more harm than none.

• Choose a cover made for your boat type and size
• Support the cover with a frame or poles so water drains off instead of pooling
• Use vents so air can circulate and moisture escapes

Gear: Boat winter covers from Taylor Made, Carver and other brands.

Quick Winterization Checklist

• ☐ Add fuel stabilizer and run the engine
• ☐ Flush the engine with fresh water
• ☐ Apply fogging oil
• ☐ Drain livewell, bilge and water lines
• ☐ Clean the bilge
• ☐ Add moisture absorbers
• ☐ Store or maintain batteries
• ☐ Install a vented, supported cover

Shop Winterization Gear

Everything above in one place: shop the TrestleThorn Winterization collection. Free shipping on orders over $99, with 30-day returns.