Learning how to winterize a 2 stroke jet ski is one of those chores that every owner dreads, but it's honestly the only way to make sure your ski actually starts up when the weather gets warm again. If you've ever spent a beautiful Saturday morning in May swearing at a seized engine or a gummed-up carburetor, you already know that an hour of work in November is worth its weight in gold. 2-stroke engines are a bit of a different beast compared to modern 4-strokes; they're simpler in some ways but way more sensitive to sitting idle for months at a time.
Leaving a 2-stroke ski out in the cold without proper prep is basically asking for trouble. Between the threat of expanding ice cracking your lines and the nightmare that is modern ethanol fuel turning into gel, there's a lot that can go wrong. But don't worry—it's not rocket science. You just need a few basic tools, some fogging oil, and a bit of patience.
Get the fuel system sorted first
The biggest enemy of a 2-stroke engine during the winter isn't actually the cold; it's the gas. Modern fuel, especially the stuff with ethanol in it, starts to break down surprisingly fast. It absorbs moisture from the air, which then settles at the bottom of your tank and turns into a nasty, corrosive mess.
Before you do anything else, you should add a high-quality fuel stabilizer to your tank. Follow the directions on the bottle, but generally, you want to make sure you have enough to treat the whole tank. Some people like to drain their tanks completely, but that can actually lead to the internal seals and gaskets drying out and cracking. Most mechanics suggest filling the tank almost to the top (leave a little room for expansion) so there's less room for air and condensation to form.
Once the stabilizer is in, run the engine for about five to ten minutes. You can do this on a flush kit in your driveway. This ensures the stabilized fuel has made its through the lines, into the fuel pump, and into the carburetors. If you skip this, the "treated" gas is just sitting in the tank while the "old" gas sits in the engine parts that actually matter.
Flushing out the cooling system
If you ride in saltwater, this step is absolutely non-negotiable. Even if you only ride in fresh water, there's likely silt, sand, or algae sitting in those cooling passages. You want to get all that junk out before it has a chance to harden into a crust over the winter.
Connect your garden hose to the flush port, but remember the golden rule of jet skis: engine on first, then water on. If you turn the water on while the engine is off, you risk flooding the cylinders with water, which is a fast way to ruin your day. Let it run for a few minutes to clear everything out.
When you're done, turn the water off first, then blip the throttle a couple of times to blow out any remaining water from the exhaust, and then shut the engine down. You want that cooling system as empty as possible.
Fogging the engine is the secret sauce
This is the part where 2-stroke maintenance really differs from 4-strokes. Because a 2-stroke engine uses the crankcase to move fuel and air, the internal bearings and the crankshaft are constantly exposed to whatever is in the air. If you just let it sit, the leftover moisture in the crankcase will cause the bearings to rust. Once those bearings pit, your engine is on a countdown to total failure.
You'll need a can of fogging oil for this. While the engine is running (during that final flush we talked about), you'll want to spray the fogging oil directly into the air intake or the carburetor throat. You'll notice the engine starts to cough and produce a ton of thick, white smoke—that's exactly what you want. Keep spraying until the engine almost stalls out, then shut it down.
This coats the entire inside of the engine—the crank, the rods, and the cylinder walls—in a thick layer of protective oil that won't run off over time. It's the single best thing you can do for a 2-stroke.
Don't forget the cylinders and spark plugs
Even after fogging through the intake, I always like to do a little extra for the top end. Pull your spark plug wires off and then remove the plugs themselves. Take your fogging oil and give a good two-second spray directly into each spark plug hole.
With the plugs still out, hold the stop button (or pull the safety lanyard) and crank the engine over for just a second or two. This moves the pistons and spreads that oil evenly across the cylinder walls and rings. While you've got the plugs out, take a look at them. If they're fouled or look nasty, just toss them and buy a new set for the spring. It's cheap insurance.
Pro tip: When you're cranking the engine with the plugs out, make sure the spark plug wires are grounded or tucked away. You don't want a stray spark igniting any of that fogging oil mist coming out of the holes.
The antifreeze "insurance policy"
Even if you think you blew all the water out of the exhaust, there's always a little bit hiding in the nooks and crannies of the water box or the head. In freezing temperatures, that water expands, and that's how you end up with a cracked manifold.
A lot of guys like to use a small section of hose and a funnel to pour some RV antifreeze (the pink stuff, not the green automotive stuff) into the cooling system. Pour it in until you see pink slush or liquid coming out of the exhaust or the pisser. This gives you peace of mind that even if there's liquid trapped inside, it's not going to freeze and break anything.
Battery care and storage
Batteries and cold weather are a terrible match. If you leave your battery in the ski all winter, there's a 90% chance it'll be dead by March. Take the time to disconnect the cables (negative first!), pull the battery out, and bring it inside where it's warm.
Stick it on a battery tender or a trickle charger in your garage or basement. Don't just leave it on the concrete floor, as that can actually drain them over time. A healthy battery should stay topped up all winter, saving you the eighty bucks for a new one next season.
Grease it up and tuck it in
Before you throw the cover on, grab a grease gun and hit any zerk fittings on the driveline. This pushes out any water that might be sitting in the bearing carrier. I also like to take a can of silicone spray or a light lubricant like WD-40 and lightly coat the metal parts of the engine and the throttle linkages. It prevents that white oxidation from forming on the aluminum components.
Finally, give the whole ski a good wash and wax. It sounds overkill, but road salt (if you're trailering it) or leftover lake scum can eat into the gelcoat if left for months. Once it's clean and dry, put a breathable cover on it. If you're storing it outside, try to keep it tilted slightly upward so any rain or melting snow drains out of the footwells rather than pooling.
Doing all of this might feel like a hassle when it's 40 degrees outside and you just want to go back inside and watch football, but your future self will thank you. When that first hot day of spring hits, you won't be the guy stuck in the garage—you'll be the one hitting the water while the engine purrs like it never even took a break.