Whether you’re hauling out, storing your boat for months, or boating year-round, winterizing is one of the smartest investments you can make in your vessel’s health.
Winterizing protects your engine, plumbing, and onboard systems from freezing temps, corrosion, and mold — and it makes spring commissioning a whole lot smoother.
Below is a simple, no-nonsense guide to help you winterize your boat based on best practices from marine organizations, towing services, and experienced boaters.
No matter your climate or boat type, these steps will keep your vessel safe until warmer weather returns.
1. Start With the Engine — Your #1 Priority
Water left in an engine can freeze, expand, and ruin entire components. These repairs can run into the thousands. Winterization always starts here.
The basics:
- Flush and drain the cooling system: Get rid of salt, sediment, and residual water.
- Change the engine oil and filters: Old oil turns acidic over time, so storing your engine with clean oil protects seals and internal components.
- Add fuel stabilizer and run the engine: Stabilizer prevents varnish and gum buildup that causes hard starts in spring.
- Fog the engine, if recommended for your boat. Fogging oil coats internal metal parts helps prevent corrosion.
- Inspect the fuel lines: Replace anything brittle or cracked.
Cold climates (Midwest, Northeast, Canada):
Make sure the engine reaches operating temperature before flushing with antifreeze. A warm thermostat ensures antifreeze enters the block.
Warm climates (South Florida, Gulf Coast):
You may not need antifreeze, but you do need to protect against corrosion. Many year-round boaters skip the deep winterization but still:
- Stabilize fuel
- Flush the engine
- Do a mid-season oil change
- Inspect cooling water flow
Salt and neglect lead to corrosion. Don’t gamble.
2. Stabilize and Protect the Fuel System
Fuel only stays fresh for a short period. Without stabilizer, it breaks down and clogs filters, injectors, and carbs.
- Fill the tank 95–100% full to reduce condensation
- Add a marine-grade stabilizer
- Run the engine 10–15 minutes to circulate treated fuel
- Replace water-separating and fuel filters
For boats stored far away (common for snowbirds or boaters storing out of state):
Always add stabilizer before transport or storage. Fuel left untreated over 6+ weeks is a top cause of springtime no-start issues.
3. Drain Freshwater and Plumbing Systems
Any system that holds water can freeze and crack, sometimes invisibly.
Drain or protect:
- Sinks
- Transom showers
- Freshwater tanks
- Washdown systems
- Livewells
- Water heaters
- Air conditioning raw-water lines
After draining, pump marine antifreeze into plumbing lines as recommended by your manufacturer.
If you store your boat indoors:
Still winterize. Enclosed sheds can drop below freezing, and boats can hold pockets of water.
For boats stored far from home
Leave yourself a note with everything you winterized and anything you left onboard. When you’re managing a boat 500+ miles away, documentation saves you from surprising spring leaks.
4. Protect All Remaining “Wet” Systems
Many boaters forget small systems that can still trap water:
- Raw water washdowns
- Bilge pumps
- Toilets and holding tanks
- Scuppers
- Bait and fish boxes
Even with mild winters, trapped water can cause mold, mildew, and funky smells — and no one wants that welcome-back surprise.
5. Clean, Declutter & Dehumidify
Winter is the perfect time to deep clean:
- Wash the hull and topsides
- Clean vinyl, non-skid, and interior surfaces
- Remove cushions, food, valuables, and electronics
- Wax fiberglass and waterproof canvas if needed
A clean, dry boat over winter means far less work in spring.
Consider running a small marine dehumidifier. Mold loves moist, wet conditions. Beyond the unpleasant cosmetic damage, humidity can wreak serious havoc on your boat. Excess humidity can destroy hull structures, rot wood cores, and corrode electronics — in addition to coating your interior spaces in mold and mildew.
6. Choose the Right Storage Setup
Your winter storage path depends on your climate and usage.
Cold northern climates:
- Shrink-wrap or use a tight, vented winter cover
- Store with the drain plug removed
- Consider adding steel wool or Brillo pad to the drain plug opening to keep rodents out
- Place dehumidifier or moisture absorbers in the cabin
Warm or humid climates (Florida, Gulf Coast):
Winterization is lighter, but mold prevention is everything:
- Vent covers well
- Use dehumidifiers or moisture absorbers
- Flush engines after every use
- Check bilge and hoses mid-season
Boaters who store remotely:
Do a final photo walkthrough and keep a checklist handy; this will makes spring recommissioning fast and stress-free.
7. Winterize Your ClearLine or ElectroStrainer System
If your boat has ElectroSea® ClearLine® or ElectroStrainer®, winterization is easy — but must be done correctly to protect the system.
You can follow detailed step-by-step instructions on winterizing your system.
👉 How to Winterize ClearLine or ElectroStrainer
This guide walks you through:
- Purchasing a maintenance lid
- Pump flushing
- Cell replacement considerations
- Spring recommissioning
- Important considerations
If your boat has a ClearLine® or ElectroStrainer®, make sure to winterize your system correctly to keep it running in tip-top shape and protect your investment.
Winterizing isn’t fun, but it is essential and it doesn’t have to be complicated.
Whether you boat on frozen lakes or sunny Florida canals, taking the time to flush, drain, stabilize, and protect every water-holding system will save you time, money, and headaches in spring.
A well-winterized boat starts easily, smells fresh, and gets you back on the water faster.
Whenever in doubt, consult:
- Your engine and equipment manuals
- A trusted marine mechanic
- Professional winterization services
Your boat deserves a safe winter, and you deserve a stress-free spring launch.