Boat Winterizing Checklist: How to Lay Up Your Boat for Winter

Quick answer: To winterize a boat, treat and top off the fuel, winterize the engine (fresh water flush, oil and gear oil change, fogging if your manual calls for it), drain or antifreeze every water system, and charge and maintain the batteries. Then clean and dry the interior, cover or shrink wrap the boat with good ventilation, and service the trailer. Your engine manual has the final word on engine steps.

Water left in an engine, a pump or a hose can freeze, expand and crack metal. Fuel that sits for months can go stale. Moisture under a cover grows mildew. A good layup prevents all three, and it makes spring commissioning faster and cheaper. Work through this checklist in order, and check off each system as you go. If you are not comfortable with engine work, have a marine technician handle the engine and do the rest yourself.

What you need

Item	Used for
Marine fuel stabilizer	Keeping stored fuel fresh
Fuel/water separator filter	Fresh filter going into storage
Flush muffs or flush port adapter	Running and flushing the engine on the trailer
Engine oil, filter and gear lube	Oil and lower unit service (use what your manual specifies)
Fogging oil	Internal engine protection, where your manual calls for it
Non-toxic propylene glycol antifreeze (RV/marine)	Freshwater, head and raw water systems
Battery maintainer or charger	Keeping batteries charged through the off-season
Moisture absorbers	Controlling humidity in the cabin and lockers
Cover or shrink wrap and tape	Keeping out rain, snow and debris
Marine grease and grease gun	Engine fittings and trailer bearings

Step 1: Fuel

1. Add marine fuel stabilizer at the storage dose on the label, before you top off so it mixes well.
2. Fill the tank to about 90 to 95 percent. This limits air space for condensation and leaves room for expansion.
3. Run the engine 10 to 15 minutes so treated fuel reaches the lines, filters and injectors or carburetor.
4. Replace the fuel/water separator element so you start spring with a clean filter.

Our marine fuel additive buying guide covers which treatment to use and how ethanol fuel causes problems in storage.

Step 2: Engine

1. Flush the cooling system with fresh water, especially if you run in salt or brackish water.
2. Change the engine oil and filter while the engine is warm. Used oil contains acids and moisture that you do not want sitting all winter.
3. Drain and refill the lower unit or sterndrive gear oil. Milky or creamy oil means water is getting in, so have the seals checked before storage.
4. Fog the engine if your owner's manual calls for it. Procedures differ by engine type and maker.
5. Drain the raw water cooling system completely, or fill it with antifreeze, following the manual for inboards and sterndrives.
6. Grease all fittings, spray exposed metal with a corrosion inhibitor and check belts and hoses.
7. Inspect the propeller and the anodes. Replace anodes that are about half worn.

Running an outboard? Follow our step-by-step guide on how to winterize an outboard motor. For anodes, see the marine anode and zinc buying guide.

Step 3: Water systems

1. Freshwater: Drain the tank and water heater, bypass the water heater if fitted, then pump non-toxic propylene glycol antifreeze through until it runs pink at every faucet and shower.
2. Head: Pump out the holding tank, flush with fresh water, then run antifreeze through the head, hoses and macerator.
3. Livewells, washdown and baitwells: Drain fully and run antifreeze through the pumps and lines.
4. Air conditioning and generator: Follow the maker's winterizing procedure for raw water circuits.

Never use automotive (ethylene glycol) antifreeze in potable water or anything that drains overboard.

Step 4: Batteries

1. Fully charge every battery.
2. Turn the battery switch off, or disconnect the negative cables, to stop small drains.
3. Connect a marine battery maintainer, or remove the batteries and store them somewhere cool and dry, then top them up periodically.
4. Clean the terminals and apply a corrosion protectant.

Our marine battery charger buying guide explains maintainers versus onboard chargers.

Step 5: Bilge

1. Pump out, clean and degrease the bilge so oil and debris do not sit all winter.
2. Test the bilge pump and float switch.
3. If the boat stays in the water, keep the bilge pump powered and check the boat regularly.
4. If stored on land, pull the drain plug (tie it to the key or helm so you remember it in spring) and keep the bow slightly higher so water drains.

Step 6: Interior

1. Remove electronics you can take home, plus food, drinks, flares and anything that can freeze or attract pests.
2. Clean and dry upholstery, carpets and lockers. Prop open hatches, lockers and the fridge so air moves.
3. Remove cushions if you can, or stand them on edge.
4. Place moisture absorbers in the cabin and lockers to fight mildew.

Step 7: Cover or shrink wrap

1. Wash and wax the hull and deck first. Dirt under a cover holds moisture and stains.
2. Use a fitted cover with support poles so water and snow cannot pool, or shrink wrap for a tight, snow-shedding cover.
3. Always build in ventilation. Vents prevent condensation and mildew under any cover.
4. Patch any shrink wrap tears right away with marine shrink wrap tape.

Choosing a cover? See our bimini top and boat cover buying guide.

Step 8: Trailer

1. Inspect and repack or grease the wheel bearings, and check the seals.
2. Inflate tires to the sidewall pressure and block the trailer so tires are not carrying the full load all winter, if practical.
3. Check lights, wiring, winch strap and brakes, and rinse brakes that saw salt water.
4. Lock the coupler for security.

Our trailer bearing and hub buying guide covers bearing service and replacement.

Our picks for fall layup

All in stock at Boat Supplies Direct.

Fuel

STA-BIL Fuel Stabilizer, 32 oz or Star-Tron Stabilizer + Fuel Storage, plus a fresh Attwood Fuel/Water Separator.

Batteries

ProMariner ProSport 1.5A Multi-Use Maintainer to keep a battery topped up through storage.

Interior

Star brite No Damp Moisture Absorber, 36 oz for the cabin and lockers.

Shrink wrap

Shurtape UV-Resistant Marine Heat Shrink Tape for seams and repairs.

Trailer

Star brite Marine Grade Wheel Bearing Grease.

Shop all fall layup and winterizing →

Frequently Asked Questions

When should I winterize my boat?

Before the first hard freeze where you store it. One cold night can crack an engine block or pump that still holds water, so do not wait for the forecast to turn.

Do I need to winterize my boat in Florida or other warm climates?

Freeze protection matters less, but a boat that sits for months still needs treated fuel, maintained batteries, an oil change and moisture control. Many warm-climate owners do a lighter layup.

Can I winterize my boat myself?

Yes. Most owners can handle fuel, batteries, water systems, interior and cover. Engine steps vary by model, so follow your manual or use a technician if you are unsure.

Should I store my boat with a full or empty fuel tank?

Most engine makers recommend a treated tank filled to about 90 to 95 percent. That limits condensation while leaving room for expansion. Check your engine manual.

What kind of antifreeze goes in a boat?

Non-toxic propylene glycol antifreeze made for RV and marine use. Never put automotive ethylene glycol antifreeze in potable water systems or anything that drains overboard.

Is shrink wrap better than a boat cover?

Shrink wrap gives a tight, snow-shedding cover for one season. A fitted cover is reusable. Either works if it is supported, vented and secured well.

This guide is general information. Always follow your engine and equipment manufacturers' winterizing procedures, and consult a qualified marine technician if you are unsure about any step.