If you own a boat in any climate where the temperature drops below freezing, boat winterization is the single most important maintenance job you do all year. Skip it, do it half way, or forget one water passage, and you can crack an engine block, split a heat exchanger, or ruin a fresh water pump over a single cold night. Learning how to winterize a boat properly is not complicated, but it is unforgiving. Water expands about 9 percent when it turns to ice, and that expansion does not care whether it is inside a $200 raw water pump or a $9,000 engine. This guide walks you through winterize a boat step by step, system by system, with a full boat winterization checklist, real 2026 costs, and everything you need for spring commissioning when the season comes back around.
We wrote this for two kinds of readers. If you are an owner who wants to protect your boat, you will find a complete method here, including antifreeze amounts, fogging, battery care, and storage options. If you run a yard, work as a marine mechanic, or offer mobile winterizing, this is also the demand you serve every fall and every spring, and you can list your services free so owners find you.
The whole point of boat winterization is to get every drop of water out of every system that can freeze, and to replace it with either air or non toxic antifreeze that will not expand into a solid. Almost every winter failure traces back to trapped water. A marine engine holds coolant and raw water in dozens of small passages, and those passages are the exact spots where ice forms first because the metal is thin and the volume is small.
The most common freeze failures we see reported by yards are cracked engine blocks and exhaust manifolds, split heat exchangers, ruptured raw water pumps, burst fresh water lines under the sole, cracked water heater tanks, and shattered head pumps and macerators. A cracked block on a mid size gas inboard runs $3,000 to $9,000 to replace once you count labor and gaskets. A split exhaust manifold pair is $800 to $2,500. A ruined fresh water system with lines to chase through the hull can be $600 to $1,800. Compare any of those numbers to a proper winterize that costs a few hundred dollars in materials, and the math makes itself.
Here is the part people miss. Freeze damage is not always obvious in spring. A hairline crack in a manifold might hold pressure at the dock and only fail under load two weeks into the season, after you have splashed the boat and paid the launch fee. That is why the goal is not "good enough," it is zero water left where it can freeze. Do it once, do it right, and you sleep through the cold snaps.
Timing depends on your climate, not the calendar. The rule is simple. Winterize before the first hard freeze, which means before overnight temperatures reach the high 20s Fahrenheit for a sustained stretch. Here is a rough map for North America and comparable climates:
If you keep the boat in the water year round in a freezing climate, your risk is different but not gone. A running block heater, a bubbler system, or a heated engine space can help, but a hard, extended freeze with a power outage will still find any trapped water. In water storage in a cold climate is its own topic, and most owners in the northern tier haul out for good reason.
Before you touch a wrench, it helps to think in terms of systems rather than a single chore. Every one of these holds water, and every one needs its own treatment. Work through them in order and check each one off:
Miss one of these and you have left a water passage exposed. The livewell pump and the raw water washdown are the two most commonly forgotten. Now let us go system by system.
Understand your antifreeze before you start, because using the wrong kind is a real mistake. There are two entirely different products, and they are not interchangeable.
Propylene glycol (marine antifreeze, the pink stuff). This is the non toxic antifreeze you run through raw water systems, fresh water plumbing, heads, and any circuit that could ever contact people, fish, or the environment. It is sold by burst rating: a "minus 50" or "minus 60" rating means the fluid will slush but not fully solidify and split fittings down to that temperature. Do not confuse burst point with freeze point. A minus 50 antifreeze may start to gel around minus 10, but it will not expand enough to crack anything until far colder. For most of the country, minus 50 propylene glycol is plenty. In the far north, step up to minus 60 or even minus 100 for exposed systems.
Ethylene glycol (automotive green or the coolant in your closed loop). This is toxic and belongs only inside a sealed engine coolant loop that never touches raw water or the environment. Never pour ethylene glycol through a raw water system, a head, or fresh water plumbing.
How much pink antifreeze do you need? A rough planning figure per boat:
Buy more than you think you need. Running short in the middle of the job, with a half winterized engine, is how mistakes happen. Leftover propylene glycol keeps for years.
The engine is the expensive part, so this is where care pays off most. How you do it depends on whether you have raw water cooling or closed (fresh water) cooling.
A raw water cooled engine pulls lake or sea water straight through the block and dumps it out the exhaust. There is no coolant loop. Your job is to flush the salt or minerals, then pull antifreeze all the way through until it runs pink out the exhaust.
Drain points matter as a backstop. Even after running antifreeze, open the block and manifold drain plugs (petcocks) to confirm fluid flows out, then close them. On some engines antifreeze does not fully reach every low pocket, and the physical drain is your insurance.
A closed cooling engine has two loops. The coolant loop circulates ethylene glycol coolant through the block and is protected year round as long as the coolant is at the right mix, so test it with a refractometer and confirm it protects to at least minus 34. The raw water loop still pulls outside water through the heat exchanger, and that side must be winterized exactly like a raw water engine: draw pink propylene glycol through the raw water circuit until it runs pink out the exhaust.
Also inspect the coolant. If it is more than two or three years old, replace it. Old coolant loses its corrosion inhibitors and becomes acidic, which eats away at the heat exchanger and the block from the inside.
Fogging coats the cylinder walls, rings, and valves with oil so they do not rust over the layup. Bare cylinder walls flash rust in a matter of weeks in a damp winter, and that rust scores the rings on spring startup. Fogging oil comes in a spray can.
On a carbureted or throttle body engine, spray fogging oil into the air intake while the engine runs at fast idle, until it stumbles and blows white smoke, then let it stall on the fog. On a fuel injected engine, follow the manufacturer method, which usually means pulling plugs and spraying fogging oil directly into each cylinder, then turning the engine over by hand a few times to spread it. On an outboard, most have a dedicated fogging procedure in the owner manual. Fog after you have run the antifreeze so you finish with an oiled, water free engine.
The three drive types winterize differently, so know which you have.
Outboards. An outboard largely self drains when tilted fully down, because the water follows gravity out the lower unit. That built in drainage is why outboards are the most freeze tolerant. Still, do the full job: flush with fresh water on muffs, run antifreeze through if the motor has any water passages that hold, fog the cylinders, change the lower unit gear oil (and check that drained oil for water, which shows up as a milky color and means a bad seal), grease the fittings, and store the motor tilted down so no water sits in the leg. Stabilize the fuel or run the carbs or VST dry depending on the model.
Inboards. A straight inboard has the engine mounted in the hull with a shaft through the bottom. Winterize the raw water side as above, change oil and filter, fog, and do not forget the transmission fluid and the raw water strainer, which you should empty and clean.
Stern drives (I/O). A stern drive combines an inboard engine with an outdrive leg. This is the setup that suffers the most freeze damage because it has the most water passages and the most low pockets. Winterize the engine raw water side, but also drain the outdrive fully, change the outdrive gear oil (again checking for water), and lubricate the drive per the manual. Raise or lower the drive to the storage position specified for your model so trapped water drains. The bellows, gimbal bearing, and U joints should be inspected here too, because you have the drive apart anyway.
Fuel goes bad over a long layup. Modern pump gas with ethanol absorbs water from the air, and that water separates out and sits at the bottom of the tank, which is exactly where the pickup draws from in spring. Ethanol also degrades and gums up carburetors and injectors.
The standard approach: fill the tank to about 95 percent full to minimize the air space where condensation forms, and add a fuel stabilizer at the dose on the bottle. Run the engine for 10 to 15 minutes after adding stabilizer so treated fuel reaches the carburetor or injectors and the fuel rail, not just the tank. For diesel, add a diesel specific stabilizer and a biocide, because diesel tanks grow microbial "diesel bug" at the fuel and water interface, and that growth clogs filters and injectors. A full tank and a biocide starve and treat that growth over the winter.
Replace the fuel filter and water separator element as part of the job, or at minimum drain the water separator bowl. Starting spring with a fresh filter means one less thing to fail on the first outing.
The fresh water system is easy to winterize and easy to forget a piece of. Every line, the pump, the water heater, and every fixture holds water.
The marine head and holding tank hold water and waste, and both can freeze and crack. Pump out the holding tank at a station first. Then flush the head thoroughly with fresh water, and finally pull propylene glycol through the head by pouring it into the bowl and pumping it through so the pump, the discharge hose, the joker valve, and the holding tank inlet are all protected. Add a couple of quarts of antifreeze to the holding tank itself through the toilet so any residual liquid in the tank will not freeze. If you have a macerator or an overboard discharge pump, run antifreeze through that circuit too until it comes out pink.
Battery care over winter decides whether you buy new batteries in spring. A fully charged lead acid battery resists freezing down to roughly minus 75 Fahrenheit, but a discharged one can freeze and crack its case at only about 20 degrees, because the electrolyte in a dead battery is mostly water. So the first rule is: store batteries fully charged.
Marine air conditioning and many marine refrigeration units are raw water cooled, meaning they pump outside water through a condenser. That circuit freezes just like the engine. Winterize it by running propylene glycol through the AC raw water pump and condenser until pink flows out the discharge, usually by dropping the pump intake into a bucket of antifreeze and running the unit briefly, or by using the built in winterizing port if the system has one.
Then hunt down every other raw water circuit on the boat, because each is a freeze risk. The usual suspects are the raw water washdown pump and hose, the livewell and baitwell pumps, the deck washdown, the anchor washdown, and any raw water feed to a generator. Run antifreeze through every one until it comes out pink. The generator has its own raw water side that you winterize exactly like the main engine, including fogging if it will sit long.
Here is the full boat winterization checklist in table form. Print it, work top to bottom, and check off each system. This is the same order a good yard follows.
| System | Action | Product / amount |
|---|---|---|
| Engine oil | Change oil and filter while warm | Correct grade per manual |
| Engine raw water | Run antifreeze until pink at exhaust; open block and manifold drains as backup | Propylene glycol, 3 to 5 gal typical |
| Engine coolant (closed cooling) | Test mix with refractometer; replace if over 2 to 3 years | Ethylene glycol coolant, protects to minus 34 or better |
| Cylinders | Fog through intake or spark plug holes | Fogging oil spray |
| Fuel | Fill to 95 percent, add stabilizer (plus biocide for diesel), run 10 to 15 min | Stabilizer per bottle dose |
| Fuel filter / water separator | Replace element or drain bowl | New filter element |
| Fresh water tank and lines | Drain, then pull antifreeze through every fixture, hot and cold | Propylene glycol, 2 to 6 gal |
| Water heater | Bypass and drain, or fill with antifreeze if no bypass | Bypass kit or 6 to 10 gal |
| Head and holding tank | Pump out, flush, pull antifreeze through pump and discharge | Propylene glycol, 2 to 4 gal |
| Batteries | Charge fully, clean terminals, place on maintainer | Distilled water for flooded; maintainer |
| AC / refrigeration (raw water) | Run antifreeze through condenser until pink | Propylene glycol, 1 to 3 gal |
| Washdown, livewell, generator raw water | Run antifreeze through each until pink | Propylene glycol, 1 to 2 gal each |
| Outdrive / lower unit (I/O and outboard) | Drain and refill gear oil, check for water, grease fittings | Marine gear lube |
| Bilge and sea strainers | Empty and clean strainers, dry bilge, antifreeze in bilge low point | Propylene glycol, splash |
| Interior | Clean, remove valuables and food, prop cushions, add moisture absorbers | Desiccant tubs |
| Hull and canvas | Wash, wax, remove and store canvas, cover or wrap | Cover or shrink wrap |
Once the systems are done, the boat has to sit somewhere for months. Where and how you store it affects both cost and how much work spring commissioning takes.
Shrink wrapping seals the boat in a tight plastic skin that sheds snow and blocks water and wind. A properly wrapped boat with vents installed stays dry and comes out clean in spring. The downsides are cost, that it is single use plastic (though many yards now recycle it), and that a bad wrap job without vents traps moisture and grows mildew. Expect $18 to $28 per foot in 2026 for professional shrink wrap, so $360 to $700 for a 20 to 25 foot boat. We cover this in depth in our boat shrink wrap guide with costs and DIY tips if you want to weigh doing it yourself.
A reusable custom canvas cover or a heavy poly tarp over a frame is cheaper over several years than shrink wrap you buy new each fall. The trade off is that tarps flap, chafe, hold water in low spots, and need checking after every storm. A well built frame that sheds snow is the difference between a cover that protects and one that collapses onto your windshield in February.
Indoor heated or cold storage is the gold standard for protecting the finish, the gelcoat, and the systems, and it makes spring commissioning shorter because the boat stays clean and dry. It is also the most expensive option and the hardest to get, since indoor space fills early. Cold (unheated) indoor storage still protects from snow, UV, and wind at lower cost than heated. For the full breakdown of storage types, dry stack, and what each costs, see our boat and yacht storage guide covering dry stack and costs.
Whichever you choose, prop the boat cover or wrap high enough for airflow, install vents, place moisture absorbers inside the cabin, and leave lockers and the fridge cracked open so air moves and mildew stays away.
Spring commissioning, also called recommissioning, is winterization in reverse plus a full safety and readiness check. Do not rush it. The boats that break down on the first weekend are almost always the ones that got splashed without a proper commissioning. Give yourself a full day and work through it methodically.
Flush every drop of antifreeze out of the fresh water system before you use it, even non toxic pink. Drain the antifreeze, refill the fresh water tank with clean water, and run every fixture until the water runs clear and stops tasting or smelling of antifreeze. Reconnect the water heater bypass so the heater fills. Sanitize the tank with a diluted bleach solution or a marine tank sanitizer, then flush again, because a season of sitting grows odors and biofilm in the lines.
Spring is the right time to go through safety gear, because the season starts here. Check the expiration dates on flares (they are good for 42 months from manufacture, so many expire without you noticing). Confirm you have the right number of life jackets in good condition, and that the throwable is aboard. Inspect and weigh or replace the fire extinguishers, and note that older extinguishers are being phased out of compliance, so verify yours are current. Test the bilge pump and its float switch by hand. Test the horn, the navigation lights, and the VHF radio, and do a radio check. Service or repack the life raft if you carry one and it is due. Confirm registration is current and the numbers and decals are legible.
Inspect the hull below the waterline for blisters, cracks, or damage. Check the zincs (sacrificial anodes) and replace any that are more than half gone, because they protect your underwater metal from galvanic corrosion all season. If the bottom paint is due, this is the window to do it. Reinstall the drain plug (the transom plug is the single most forgotten item at every ramp in the country, so make a habit of it). Grease the trailer bearings and check the trailer tires, lights, and straps before the tow. Once splashed, stay at the dock for the first run, watch for leaks around every through hull and the stuffing box, confirm the engine reaches normal operating temperature and cooling water flows strong out the exhaust, and check the bilge for water before you head out.
Plenty of owners winterize their own boats, and if you are handy and have the space, it is satisfying and saves real money. The materials for a mid size boat run $150 to $350 (antifreeze, oil, filters, fogging oil, stabilizer), against a yard bill several times that. DIY also means you know exactly what was done.
The case for a yard is stronger than it looks, though. A yard carries insurance, so if they crack a block, they own it. They do it in an afternoon what takes a first timer a full day of chasing YouTube videos in a cold garage. They have the muffs, the pumps, the lift, and the disposal setup. And they will catch problems, a weeping manifold, a soft hose, a bad impeller, before those problems become a spring breakdown. For complex boats with twin engines, generators, AC, and full plumbing, most owners come out ahead paying a pro, because one missed water passage costs more than the whole winterize.
A middle path that works well: do the easy systems yourself (fresh water, head, batteries, interior) and hire out the engine and drive work where a mistake is expensive. Whatever you decide, if you want a broader picture of keeping a diesel healthy through the seasons, our marine diesel engine maintenance checklist pairs well with this guide.
Here are realistic 2026 numbers. Yard winterize pricing varies by region and by how many systems you have, but this table reflects typical full service winterization (engine, plumbing, and basic systems) versus doing it yourself. Storage and shrink wrap are separate line items on top.
| Boat size / type | DIY materials | Yard winterize (full service) | Shrink wrap (add on) |
|---|---|---|---|
| Small outboard (under 20 ft) | $60 to $150 | $150 to $350 | $250 to $450 |
| Mid size I/O or inboard (20 to 28 ft) | $150 to $350 | $400 to $800 | $360 to $700 |
| Cabin cruiser, single engine (28 to 35 ft) | $300 to $500 | $700 to $1,400 | $650 to $1,000 |
| Twin engine cruiser with generator and AC (35 to 45 ft) | $500 to $900 | $1,400 to $3,000 | $900 to $1,600 |
| Large yacht (45 ft and up) | Not typical DIY | $3,000 to $8,000+ | $1,600 to $4,000+ |
Add winter storage on top of these figures. Outdoor yard storage commonly runs $30 to $60 per foot for the season, cold indoor storage $50 to $100 per foot, and heated indoor storage $100 to $200 per foot or more. Spring commissioning at a yard usually runs a bit less than fall winterization for the same boat, often 60 to 80 percent of the winterize cost, plus the launch or splash fee.
The best time to book a yard is early, because slots and indoor space fill fast in the fall, and every owner in your region is calling the same weekend the forecast turns cold. Do not wait for the first freeze warning to start looking.
Yacht Service Network is a free marketplace and directory built for exactly this. Search yards, marinas, mobile mechanics, and winterizing services in your area, compare what they offer, read what other boaters say, and contact them directly with no fees and no markup. There is no middleman taking a cut, so the price you agree on is the price you pay. Post what you need, whether that is a full winterize, just an engine job, shrink wrap, or spring commissioning, and let local pros come to you.
Prefer your phone? Get the Yacht Service Network app and manage quotes and messages from the dock.
Heated indoor storage protects against freeze damage as long as the heat never fails, but a power outage or a heater breakdown during a cold snap can still crack a block full of water. Most yards winterize the water systems anyway as cheap insurance, and you should too. The fuel stabilizer, oil change, and fogging steps also matter regardless of temperature, so heated storage is not a reason to skip the whole job.
A small outboard with little plumbing might use 1 to 2 gallons. A mid size boat with an engine raw water side, fresh water plumbing, and a head typically needs 4 to 8 gallons. A large boat with twin engines, a generator, a water heater, AC, and full plumbing can use 12 to 20 gallons or more. Always buy a couple of extra gallons so you never run short mid job, since leftover propylene glycol keeps for years.
The pink stuff is propylene glycol, which is non toxic and goes through raw water systems, fresh water plumbing, and heads. Automotive green (or the coolant in a closed loop) is ethylene glycol, which is toxic and belongs only inside a sealed engine coolant loop that never touches raw water or the environment. Never run ethylene glycol through a raw water or fresh water system.
Outboards are the most freeze tolerant because they largely drain by gravity when tilted down, but they still need the full treatment: fresh water flush, fogging the cylinders, changing the lower unit gear oil, greasing fittings, and stabilizing the fuel. Skipping the fogging and the gear oil change is how outboards develop internal rust and seal problems even without a freeze crack.
Before the first sustained hard freeze, when overnight lows reach the high 20s Fahrenheit for more than a night or two. In the northern tier that means mid October to mid November, in the mid Atlantic late October through November, and in the upper South November into early December. Watch your local forecast rather than the calendar, and finish before a cold snap catches the boat still full of water.
Several tie for first place: the raw water washdown and livewell pumps, the water heater (which cracks if not drained or filled with antifreeze), the shower sump, and the drain plugs left open in fall then forgotten in spring. On the spring side, reinstalling the transom drain plug before launch is the single most forgotten item at boat ramps everywhere, so build a habit around it.
DIY materials for a mid size boat run $150 to $350, versus $400 to $800 for a full yard winterize, so DIY is cheaper if you have the space, the tools, and the time. The yard is worth the money for complex boats or if you would rather have insured pros catch problems before spring. A common compromise is doing the simple systems yourself and paying a mechanic for the engine and drive work where a mistake is expensive.
Spring commissioning, or recommissioning, is winterization in reverse plus a safety check: flushing out the antifreeze, replacing the raw water impeller, checking all fluids and belts, reconnecting and testing batteries, going through safety gear and expiration dates, checking zincs and the hull, and doing a careful first launch watching for leaks. Handy owners can absolutely do it, but book a yard early if your list is long or your boat is complex.