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How to Winterize a PWC (Jet Ski) for Off-Season Storage

How do I fog, stabilize, and store my jet ski so it's ready next season?

A PWC dies over winter from three things, not the cold itself: gummed-up ethanol fuel, internal corrosion on bare metal, and freeze damage in the cooling and exhaust passages. Winterizing is just blocking all three — stabilize and top off the fuel, fog the cylinders to coat them with oil, and flush/drain (and where required, antifreeze-protect) the cooling system before the first hard freeze. Cooling design splits by brand: most modern Sea-Doos use a closed-loop coolant system (the engine runs on coolant, dumping heat through the ride plate, with only the exhaust on a raw-water circuit), while Yamaha WaveRunners and Kawasaki Jet Skis are open-loop raw-water cooled (lake/sea water runs through the engine itself). That difference changes the freeze step — always confirm your model's exact procedure in the owner's manual.

ℹ️ Reference only: For general reference only. This guide does not guarantee any result — every home is different. Verify against your local building codes and a licensed professional before acting, especially for electrical, gas, plumbing, structural, or roof work.

💵 $40-$90 DIY (stabilizer, fogging oil, corrosion spray, antifreeze if needed; battery tender ~$30-$60 one-time). $150-$350 at a marine shop, more with an oil change or supercharger service. ⏱ 1-2 hours for a single ski once you have supplies; add 30-45 min if you also change the oil. ● Use caution
Safety: Fuel and fogging work involves explosive vapor and a running engine: work outdoors or in a well-ventilated space, never near sparks/flames, and treat the entire engine bay as an ignition-protected zone — only use marine-rated, ignition-protected accessories around fuel and the engine compartment. Running the engine produces carbon monoxide; never run it in a closed garage. Keep hands and loose clothing clear of the jet pump and impeller. Follow the flush rule exactly (engine on before water on, water off before engine off) to avoid hydrolocking the engine with water through the exhaust. Disconnect the battery negative first and never store a battery where a spark could ignite vented hydrogen.

Common causes

How to fix it

  1. Read your model's owner/service manual first. Cooling design dictates everything, and it splits by brand: most modern Sea-Doos (Rotax 4-TEC) use a closed-loop coolant circuit (engine cooled by coolant, heat dumped through the ride plate) with a separate raw-water loop cooling the exhaust, while Yamaha WaveRunners and Kawasaki Jet Skis are open-loop raw-water cooled (lake/sea water runs through the engine itself). The fogging and fuel steps are universal; the cooling/freeze step differs by design.
  2. Fill the fuel tank to about 95% and add marine fuel stabilizer (e.g., Sta-Bil Marine or your engine maker's additive) at the label dose. A near-full tank leaves little air space for condensation; stabilizer slows ethanol gumming and phase separation. Run the engine 2-3 minutes so treated fuel reaches the injectors/carb — do this on a hose flush following the flush rule in the next step (engine on first, then water).
  3. Flush the cooling system with fresh water per the manual: connect a garden hose to the flush fitting, START THE ENGINE FIRST, then turn on the water (and shut water OFF before the engine to avoid backing water into the cylinders through the exhaust). Flush ~90 seconds to clear salt/silt.
  4. Fog the engine to coat cylinders with corrosion-preventing oil. With the engine warm and running (or per manual, on some EFI models you fog after shutdown via the air intake/spark-plug holes), spray marine fogging oil into the air intake until it stalls or smokes heavily. Alternatively, pull the spark plugs, spray fogging oil into each cylinder, and crank a couple of revolutions to spread it. Reinstall plugs.
  5. Handle freeze protection by cooling type. Open-loop raw-water skis (most Yamaha and Kawasaki): after the final flush, with water OFF, blip the throttle briefly (1-2 seconds, do not over-rev — the pump runs dry) and rock/tilt the hull to purge water from the exhaust and cooling passages so nothing is left to freeze; some owners also use the manual's compressed-air or non-toxic-antifreeze step. Closed-loop coolant models (most modern Sea-Doo): confirm the engine coolant is rated to your lowest expected temp, and still protect the raw-water exhaust loop per manual (often by drawing in non-toxic RV/marine -50F propylene-glycol antifreeze).
  6. Service the battery: disconnect it (negative first), wipe terminals, coat with dielectric grease, and store it in a cool, dry place with stable temperature on a marine-rated smart maintainer/tender. (The old 'never store on concrete' rule is a myth for modern plastic-case batteries — what matters is a stable, cool temperature.) A charged battery resists freezing; a dead one can crack.
  7. Lubricate and protect: spray corrosion inhibitor (e.g., Corrosion Block / Quicksilver) on metal engine and electrical surfaces, grease the steering, throttle, and pump fittings per the lube chart, and apply marine grease to the driveshaft/pump bearing if your manual calls for it.
  8. Add fresh oil if the manual specifies an oil change for 4-stroke models (Sea-Doo 4-TEC, Yamaha 4-stroke, Kawasaki 4-stroke). Storing on fresh oil keeps acidic combustion byproducts off bearings. Top off the 2-stroke oil-injection reservoir on older 2-stroke skis.
  9. Store it right: cover with a breathable PWC cover (not a sealed tarp that traps moisture), keep it off the ground on a trailer or stand with weight off the tires, and loosely plug exhaust/intake openings with copper/stainless wool or pest mesh to block rodents (avoid plain steel wool — it rusts and stains; and tag yourself to REMOVE any plug before the first start in spring). Crack the seat or use a moisture absorber to vent the engine bay. Never seal a fuel-vapor space airtight.

DIY or call a pro?

Very DIY-friendly for a competent owner with the manual — fuel stabilizing, fogging, flushing, and battery care are an afternoon's work and the single highest-value maintenance you'll do. Hand it to a marine shop if you have a supercharged or intercooled engine you're unsure about, a closed-loop coolant system needing antifreeze service, suspect existing fuel/water contamination, or simply lack a flush setup and indoor space.

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Based on: BoatUS / BoatUS Foundation; ABYC (American Boat and Yacht Council); NMMA (National Marine Manufacturers Association); USCG Auxiliary; Sea-Doo / BRP owner and service guidance; Yamaha WaveRunner service guidance; Kawasaki Jet Ski service guidance; NFPA (boatyard/fuel fire-safety guidance)

General marine-maintenance guidance, not a substitute for a qualified marine technician or surveyor. Boats and conditions vary; for fuel, electrical, fire, or structural issues — or anything safety-critical — consult a professional. Always follow your engine and equipment manuals.