How to Winterize a Boat: The Complete Guide for Inboard & Wake Boats

By Adam Moore, SWELL Wakesurf · Updated October 2026

Every fall in Minnesota the same question comes up at the dock: what do I actually need to do to winterize my boat? This is the process I've used my whole boating life (over 40 years now) and the same one our shop uses on the wake boats we winterize every fall. It's written for inboard ski and wake boats (V-drive and direct drive), with the extra steps for ballast, heaters and showers that most guides skip.

Whether you're in Minnesota, Texas or California, if the boat is going to sit, winterize it. One cold snap with water in the block can crack it, and that's an engine replacement, not a repair.

Plan on about an hour and under $150 in materials if you do it yourself.

Quick checklist

1. Fill the tank and add fuel stabilizer
2. Change the oil and filter (engine warm)
3. Replace the engine impeller
4. Replace the ballast pump impellers
5. Change the fuel filter / fuel-water separator
6. Change the transmission fluid (and V-drive fluid)
7. Clean the raw water strainer
8. Clear the heater lines
9. Drain the engine block
10. Run antifreeze through the engine
11. Run antifreeze through the ballast system (and shower)
12. Charge and disconnect the batteries
13. Clean, dry and cover (or shrink wrap) the boat

What you'll need

• RV antifreeze: 6–8 gallons for a typical wake boat with ballast (see "How much antifreeze" below)
• Fuel stabilizer (we use Sea Foam)
• Oil and oil filter for your engine (check your manual for type and capacity)
• Oil extractor / transfer pump (we use a Topsider-style vacuum pump)
• Replacement engine impeller (for Indmar, the Johnson 09-812B kit; for Malibu M5/M6, the Johnson 09-707B) and an impeller puller
• Ballast pump impellers (see Step 4)
• Fuel filter, transmission fluid, V-drive fluid
• An engine flusher ("Fake-A-Lake" style) or a 20+ gallon tub, a small sump pump and a garden-hose adapter
• Funnels, rags, zip-top bags
• Low-pressure air source (the pump you use for tubes and inflatables, not a full-pressure compressor)
• Battery charger or tender

Step 1: Stabilize your fuel

Fill the tank completely. A full tank leaves no room for condensation to add water over the winter. Use non-oxygenated (non-ethanol) premium if you can find it, or otherwise the highest octane available.

Add fuel stabilizer at the rate on the bottle (Sea Foam is 1 oz per gallon). Don't overthink the exact amount; dose for a full tank. Add it before your last run or before you trailer the boat, so it mixes and gets pulled through the fuel lines and injectors. If your boat lives on a lift, do this on the lift before you head to the launch.

Step 2: Change the oil and filter

Always store the boat with fresh oil. Used oil carries acids and contaminants that sit on engine parts all winter. Wakesurfing means long stretches at high RPM, which is hard on oil, so I also change it every 50 hours like the manual says.

1. Warm the engine up. Hook a flusher to the water intake on the bottom of the hull with a garden hose, then run the engine to normal idle temperature (the middle of the gauge). Never run an inboard dry; the impeller and engine need water.
2. Pump the oil out. Connect the extractor hose to the oil drain hose on the engine, pull the dipstick or oil cap so it doesn't vacuum-lock, and pump until you're only getting air.
3. Swap the filter. Slip a zip-top bag over the old filter before unscrewing it, so oil doesn't drip into the bilge. Fill the new filter about half full with fresh oil, rub a little oil on the gasket, and screw it on hand-tight.
4. Refill. Add a little less than the full capacity, start the engine briefly, shut it off, then check the dipstick and top off. (On our 2005 Supra Launch, that's 5 quarts, then about another half quart.) Over- or under-filling both cause problems, so check your manual's spec.

Step 3: Replace the engine impeller

There's debate on this one. Some people say only replace it in the spring, or just inspect it. I replace it every fall and have for decades without a problem on inboards. Minnesota summers are short, and I don't want to do maintenance in July. The goal is to do nothing all summer but ride.

1. Find the raw water pump and remove the cover plate. Check the gasket or O-ring and replace it if it's flattened or torn.
2. Pull the old impeller with an impeller puller (or carefully with pliers). If any blades are missing, find the pieces; they end up in the heat exchanger or cooler.
3. Make sure the new impeller is the same part number or a direct replacement. Coat the edges with the supplied lubricant, line up the splines and push it in, bending the vanes the same direction the old ones were.
4. Reinstall the cover, then run the engine on the flusher and confirm water is coming out of the exhaust.

Shop engine impellers: Indmar (Johnson 09-812B) · Malibu M5/M6 (Johnson 09-707B) · all pump impellers

Step 4: Replace the ballast pump impellers

Most modern wake boats have reversible ballast pumps: black pumps with a brass head, and there's an impeller inside that head. I replace these every fall too, for the same reason.

• Johnson Talulah 13.5 GPM / Jabsco Ballast Puppy: replacement impeller
• Johnson Talulah HF 30 GPM: replacement impeller (S2003)
• Jabsco Ballast King: replacement impeller

Older boats may have bilge-style ballast pumps instead (one on the thru-hull for fill, one on the tank or bag for drain). Those don't have impellers and don't need this service.

Step 5: Fuel filter, transmission and V-drive

• Fuel filter / fuel-water separator: most manuals call for these every 50 hours. We put 70–90 hours a season on our boats, so they get done every fall with the oil.
• Transmission fluid: use the same extractor pump. Pull the old fluid out and refill to spec. Transmission filters rarely need service, but check your manual.
• V-drive fluid: if you have a V-drive, do the same: extract it and refill with the manufacturer's recommended oil.

Step 6: Clean the raw water strainer

Most boats built since the 2000s have a raw water strainer (a clear bowl with a metal basket) between the thru-hull and the pump. Remove the cover, drain it, clean the basket and reassemble. Leaving water in the bowl is a common reason they crack over the winter.

Step 7: Clear the heater lines

If your boat has a heater (most of ours do here in MN), this step is not optional. I learned it the hard way.

1. Find the two smaller hoses (usually about 1" diameter) running from the engine manifolds toward the bow. Those are the heater supply and return.
2. Disconnect both and blow low-pressure air through until no more water comes out. Use the pump you fill tubes with, not a shop compressor; high pressure can damage the heater core.
3. For extra protection, pour some antifreeze into one hose with a small funnel until it comes out the other end.
4. Reconnect both hoses and tighten the clamps.

Step 8: Drain the engine block

Some newer engines have block drain plugs (check your manual for their location). We usually just remove the lower hoses from the engine and raw water pump and let it drain. Once drained, reinstall the plugs and hoses and double-check every clamp. A loose clamp in the spring means a bilge full of lake.

Step 9: Run antifreeze through the engine

I like to store inboards full of RV antifreeze. It protects any water that might still be hiding in the block and keeps the inside of the engine from corroding. RV antifreeze is propylene glycol and is safe for the lake, so in the spring you can drop the boat in and go.

Never use automotive (ethylene glycol) antifreeze. It's toxic to fish and wildlife.

Here are three ways to do it, from simplest to my favorite:

Option 1: Funnel at the intake hose. Pull the raw-water intake hose off the thru-hull and have 3–4 gallons of antifreeze open and ready. Start the engine and pour antifreeze into the hose with a funnel. When pink comes out of the exhaust, shut it down and reconnect the hose.

Option 2: Engine flusher. Same idea, but pour the antifreeze into a "Fake-A-Lake" style flusher on the intake under the hull. It works, but you'll waste some antifreeze around the edges.

Option 3 (my favorite): Tub and sump pump. This is how we do it in the shop. Connect the engine's intake hose to a garden hose with an adapter, and run the garden hose to a small sump pump sitting in a 20+ gallon tub with 3–5 gallons of antifreeze. Put the tub under the exhaust. Start the engine, turn on the pump, and let it cycle for a couple of minutes until the exhaust is running solid pink. It recirculates, so nothing's wasted.

Step 10: Run antifreeze through the ballast system (and shower)

1. Drain everything. Run every ballast pump on drain until no more water comes out.
2. Add about ½ gallon of antifreeze per tank or bag. Pour it down the ballast vent with a funnel, or pull a hose or fitting and pour it in. Note: modern boats with reversible pumps usually have a check valve on the vent, so make sure the antifreeze is actually getting into the system.
3. Hit drain again to push antifreeze through the pumps and lines. Pink out the side = done.
4. Transom shower / freshwater system: if you have one, drain the tank, then run antifreeze through the pump and out the shower head until it comes out pink.

Step 11: Batteries

Fully charge the batteries, then disconnect the battery leads so nothing drains them over the winter. I've done this for years in Minnesota, where it hits 20 below, and the batteries still last their normal life. Even better: pull them and keep them on a trickle charger or battery tender for the winter.

Step 12: Clean, protect and cover

• Clean it now. Dirt, sunscreen and lake scum are much easier to remove now than after sitting all winter.
• Keep the critters out: a few dryer sheets around the boat (mice hate them).
• Control moisture: put a container of DampRid under the cover.
• Indoors: a standard cover is fine.
• Outdoors: get it professionally shrink wrapped. Vented shrink wrap sheds snow load and breathes; regular covers hold moisture, which causes mildew and problems in the spring.

How much antifreeze do I need to winterize my boat?

Where it goes	Amount
Engine (inboard V8, depending on method)	3–5 gallons
Heater lines	~½ gallon
Ballast system	~½ gallon per tank or bag
Shower / freshwater system	~½ gallon
Typical wake boat with ballast	6–8 gallons
Ski boat without ballast	4–5 gallons

Buy one extra jug. It's cheap, and running out halfway through is worse.

Video: watch us winterize an inboard boat

Have a 2021+ Nautique G21, G23, G25 or Paragon? Watch our Nautique winterizing video.

Boat winterization FAQ

When should I winterize my boat? Before the first hard freeze, meaning the first night forecast below 32°F. In Minnesota that's usually October. If you're still using the boat, at least drain the engine block and heater after any cold night.

Do I need to winterize if I live somewhere warm? If the boat will sit for months, yes. Fresh oil, stabilized fuel and charged batteries matter anywhere, and a surprise cold snap can still crack a block full of water.

Can I use car antifreeze? No. Use pink RV/marine antifreeze (propylene glycol). Automotive antifreeze is toxic and will end up in the lake in the spring.

Should I replace the impeller in the fall or the spring? Either works. We do it in the fall so the boat is ready the day the ice goes out, and so there's no maintenance during the season.

Do I need to fog the engine? Check your engine manual. Many modern fuel-injected inboards don't call for fogging; older carbureted engines usually do.

How do I winterize a wake boat vs. a regular ski boat? Same engine steps. Wake boats add the ballast system (Step 10), usually a heater (Step 7), and often a shower, all of which can hold water and crack.

How much does it cost to have a shop winterize my boat? Typically several hundred dollars, and more with impellers and fluids. Doing it yourself costs under $150 in materials and about an hour.

Want us to do it?

If you're in the Twin Cities area, SWELL Marine, our service division in White Bear Lake, MN, winterizes, shrink wraps and stores boats every fall, and can handle upgrades like ballast systems, towers, audio and Fresh Air Exhaust over the winter.

Questions? Message us on chat, visit our help desk, or email hangten@swellwake.com.