Two things can quietly ruin a PWC over the off-season, and neither one looks dramatic while it's happening. Water sitting in the cooling passages can freeze, expand, and crack the block or exhaust housing from the inside. Fuel left in the tank breaks down chemically and can leave a varnish coating that clogs injectors, carb jets, and fuel passages too small to see with the naked eye. Both problems are almost entirely preventable, and both get expensive fast if they're not caught. That's the whole case for winterizing properly — a little time in the fall saves you a much bigger repair bill in the spring.
Fall: Putting the Ski to Bed
Flush First, Then Treat the Fuel
Before touching anything else, run a fresh-water flush through the cooling system to clear out salt, sand, or lake sediment. Treating the fuel comes next, and here's the chemistry behind why it matters: gasoline, especially ethanol-blended pump gas, oxidizes and separates over months of sitting still. The lighter volatile compounds evaporate out first, leaving behind heavier, gummy residue — varnish — plus water that ethanol pulls out of the air and drops out of suspension at the bottom of the tank. That varnish doesn't just sit in the tank, either. It travels through the fuel system and can harden in the tightest passages it finds, which on a fuel-injected engine means injector tips and on a carbureted engine means jets just a few thousandths of an inch wide.
A fuel stabilizer works by slowing that oxidation reaction, essentially buying the fuel several months of shelf life it wouldn't otherwise have. Dosage matters here — too little and the fuel oxidizes anyway, too much doesn't really buy extra protection but isn't harmful either. Ratios vary by product and formulation (marine-specific stabilizers are often concentrated differently than the general automotive bottle at the auto parts store), so check the label on whatever you're using rather than assuming a one-size ratio. Once it's mixed in, run the engine for several minutes so treated fuel actually reaches the injectors or carb bowls, not just the tank.
Fogging the Engine
With the engine idling, spray fogging oil into the air intake or carburetor throat in short bursts until you see white smoke and the engine starts to stumble, then shut it down while it's still saturated with oil. That coats the cylinder walls, rings, and valve faces in a thin protective film — the barrier between bare metal and the humid air it'll sit in all winter. Bare steel and iron can start rusting almost as soon as they're exposed to damp air with nothing to protect them, and a PWC stored in an unheated garage picks up plenty of ambient moisture even if it never touches water again until spring. Skip fogging, and you're more likely to find surface corrosion on the cylinder walls come spring — the kind that shows up as scuffing or blow-by once the engine's running again.
Draining the Cooling System and Heat Exchanger
This is the step that does the most to prevent the expensive failure. Water expands roughly 9% in volume when it freezes, and inside a cast aluminum block or heat exchanger, that expansion has nowhere to go. The casting is rigid, the ice isn't compressible, and something usually gives — a crack through the thinnest wall section of the block or exchanger, which then leaks coolant or lake water into places it doesn't belong the next time the engine runs. It's the same failure mode as a car radiator without antifreeze, except a PWC's cooling passages are smaller and more convoluted, so it's easier to leave a trapped pocket of water behind by accident.
Draining alone often isn't enough, since water clings to internal passages by surface tension and doesn't always gravity-drain out of every low spot. Blowing the system out with low-pressure compressed air after draining clears the pockets gravity misses. Pay particular attention to the heat exchanger — it's a compact bundle of small passages, exactly the geometry that traps water stubbornly. If your ski runs closed-loop, antifreeze-based cooling rather than raw water through the block, follow the manufacturer's guidance on running non-toxic marine antifreeze through the system instead of relying on air alone.
Battery and Storage Position
Pull the battery and store it somewhere temperature-stable, ideally on a maintenance charger — a battery left connected to the ski's wiring harness over winter discharges slowly from parasitic draw and can freeze at a noticeably higher temperature than a fully charged one. Store the ski itself in a level, engine-neutral position per the manual, so oil and fogging residue settle where they're supposed to instead of pooling somewhere they shouldn't.
Spring: Waking It Back Up
Reinstall the Battery First
Charge it fully before reinstalling rather than trusting whatever charge it held over winter — even a battery that's been sitting on a tender for months is worth confirming with a multimeter before you rely on it to crank a cold engine.
Expect Some Smoke on First Start
The fogging oil that protected the cylinders all winter has to burn off, and it does that in the first several seconds to a minute of running. A puff of blue-white smoke and an odd smell on that first start is just the fogging oil purging, not a sign of a blown ring or head gasket. If it hasn't cleared up after a minute or so of steady running, that's when it's worth looking into further.
Inspect Every Hose You Can Reach
Rubber hoses can dry-rot in storage even without ever being near water, because the plasticizers that keep rubber flexible slowly migrate out and evaporate — especially with the temperature swings between a cold garage at night and a heated one during the day. The result is a hose that looks intact but has lost its flexibility, and cracks the first time it's flexed or pressurized. Squeeze every cooling and fuel hose you can reach, checking for stiffness, surface cracking, or a chalky texture, and replace anything that doesn't flex back easily. A hose failure at speed on the water is a much worse problem than one caught on a trailer in the driveway.
Startup Sequence Matters
It helps to have the engine in the water, or hooked to a flush attachment with the water already running, within the first 2 to 5 seconds of cranking. A couple of seconds dry at startup is normal and nothing to worry about, but the longer it runs without water, the more the impeller and seals are working without the cooling and lubrication they depend on — so it's worth having water ready to go before you turn the key. Once it's running, check the tell-tale (the small stream of water exiting the hull) to confirm flow, let it idle up to operating temperature before giving it throttle, and keep an eye out for leaks around the fittings you drained and reconnected in the fall. If everything you touched back then — clamps, drain plugs, hose connections — is torqued and seated correctly, this should be a non-event, which is exactly why the extra care during winterization pays off in the spring.
The Bottom Line
Winterizing isn't really about any single step — it's about keeping trapped water out of anywhere it can freeze, and not leaving raw fuel sitting long enough to break down. Everything else on the checklist supports one of those two goals. Do it in the right order each fall, give it a thorough look each spring, and the ski that comes out of storage will run exactly like the one that went in.
Photo: Onesojourner, Wikimedia Commons (public domain)