Winterizing Your Outboard: The Complete Off-Season Checklist by Brand

Skipping winterization — or rushing it — is one of the most expensive mistakes a boat owner can make. Trapped water cracks blocks, stale fuel gums up carburetors and injectors, and a water pump that sat dry all winter can fail the moment you launch in spring. Here's a full checklist, plus the quirks that differ by engine brand.

The core checklist (every outboard)

1. Stabilize and run the fuel. Add fuel stabilizer to the tank, then run the engine long enough to circulate treated fuel through the carburetor or injectors before shutdown.
2. Change the engine oil and filter (4-strokes). Used oil holds acidic combustion byproducts that will sit against internal components all winter. Change it before storage, not after.
3. Fog the cylinders (carbureted 2-strokes). Fogging oil coats cylinder walls and prevents corrosion during months of inactivity.
4. Change the lower unit gear lube. Milky or cloudy lube means water intrusion — a seal problem worth catching now rather than after a freeze.
5. Inspect the water pump impeller. A worn impeller is cheap insurance against overheating; many shops replace it every 2–3 seasons regardless of visible wear.
6. Pull and inspect the spark plugs. Fouled or worn plugs are easy to spot now and far easier to replace before storage than to diagnose as a no-start in spring.
7. Flush the cooling system with fresh water to clear salt, sand, or debris, and make sure all water is drained from the block before freezing temperatures hit.
8. Disconnect or maintain the battery. Either remove it to a warm, dry space on a maintainer, or leave it connected to a marine battery tender.
9. Grease fittings and moving linkages, and coat the powerhead with corrosion inhibitor.
10. Store the prop off, or protect it, and note this is a good time to check for fishing line wrapped around the prop shaft seal.

Brand-specific notes

Mercury / Mercruiser

Mercury's 4-strokes are straightforward oil-and-filter jobs; carbureted 2-stroke Mercs need fogging through the carburetor throat while running, followed by a final short burst of fogging oil right at shutdown. Mercruiser sterndrives add a second layer: drain the block and manifolds completely, or run non-toxic antifreeze through the raw water system if the boat stays in a freezing climate. Browse Mercury/Mercruiser parts.

Yamaha

Yamaha four-strokes use a VST (vapor separator tank) fuel system; run stabilized fuel long enough that it reaches the VST, not just the primer bulb line. Yamaha's factory fogging oil is applied through the air intake at idle. Browse Yamaha parts.

Johnson / Evinrude

Evinrude E-TEC owners hear that these engines are "self-winterizing" — the direct-injection design does reduce some traditional fogging needs, but you should still run the built-in winterization mode (holding the mode button per your owner's manual), change gear lube, and check the water pump. Carbureted Johnson/Evinrude models need full fuel stabilization and fogging like any carbureted 2-stroke. Browse Johnson/Evinrude parts.

Suzuki & Honda

Both are 4-stroke-only lines, so the priority is oil and filter change plus a full cooling system flush — Honda's BF and Suzuki's DF series are both sensitive to salt buildup in the water passages if not flushed thoroughly. Browse Suzuki parts and Honda parts.

Tohatsu / Nissan & Chrysler / Force

Many of these engines are older or carbureted; budget extra time for carburetor-circuit fuel stabilization and fogging, and inspect fuel lines and primer bulbs for cracking, which is common on engines over 10 years old. Browse Tohatsu/Nissan parts and Chrysler/Force parts.

Volvo Penta

Sterndrive systems need the same full block-and-manifold draining as Mercruiser, plus attention to the drive unit gear lube and bellows inspection before covering for the season. Browse Volvo Penta parts.

Sea-Doo, Kawasaki, Polaris & Tigershark (PWCs)

PWC engines winterize similarly to outboards — stabilize fuel, fog or oil-change per your model, flush with a flush kit or muffs, and drain the exhaust system completely, since PWCs sit closer to horizontal and trap water more easily than an outboard's vertical exhaust. Also fully drain and dry the hull to prevent freeze damage to hoses and fittings. Browse Sea-Doo, Kawasaki, Polaris, and Tigershark parts.

Parts worth having on hand

Even if nothing's failed yet, winterizing is the easiest time to replace wear items before they strand you in spring: a fresh spark plug set, a new water pump impeller, and gear lube. Checking these off now means your first trip out isn't a maintenance trip.

FAQ

Do I really need to winterize if I live somewhere that doesn't freeze?
Fuel stabilization, oil changes, and fogging still matter in mild climates — stale fuel and unprotected cylinders cause problems whether or not it freezes. Skipping the antifreeze/draining steps is usually fine if temperatures genuinely never approach freezing.

How long can fuel sit with stabilizer added?
Most stabilizers are rated for storage periods of several months up to about a year, but always check the product label for your specific stabilizer.

Can I winterize myself, or should I use a shop?
Most of this checklist is DIY-friendly with basic tools. If your engine needs antifreeze circulated through a sterndrive or has a complex fuel-injection purge procedure, a shop visit or your owner's manual's specific steps are worth the extra care.

Photo: Boats moored at a boatyard in the off-season, Paubritton100, licensed under CC BY-SA 3.0, via Wikimedia Commons.