It's important to understand that everyone does "winterizing" differently. Also what do we mean by winterizing? Because technically speaking, that's ensuring your boat is ready for a longer storage period, potentially below freezing temps. To others, it means doing maintenance as well.
With that being said, here is my checklist I do every year which includes maintenance. I do it in this order so that the oil is warm when you get to the oil change. Many get by with just air instead of antifreeze but most boaters that go well into freezing temps use antifreeze instead since it's cheap and effective and reduces any risk of leaving any water in the system. Also, if you don't have a compressor, it's cheaper to buy a drill pump.
- Add fuel stabilizer & fill tank first.
- Drain coolant from ride plate. Fill coolant reservoir and as it comes out the ride plate, replace drain plug (73 in-lbs) so that there's no air in the system (this should be done every 2 years only). Make sure level sits between min/max on reservoir and confirm after engine has been ran later.
- Antifreeze exhaust flush using drill pump. Start engine first. Purge leftovers by revving engine. Use 2 gallons (I would use 4 if I had an intercooler). Capture antifreeze with kids swimming pool. Easy to then pump it back into the jug and dispose of in the toilet.
- Check oil level (used to confirm your oil level isn't too low).
- Suck oil out through dipstick (18.75" tube length) using a vacuum pump. This takes a while 15-20 min. Be patient.
- Run engine a few seconds then pump some more to get more oil out.
- Remove bolt holding filter, cover and pull filter to drain. E10 socket.
- Install new filter, install and lube O ring. Also clean old oil around filter area.
- Add fresh oil (˜3 quarts), do half of last quart then check level.
- Reinstall dip stick and run engine for a few seconds. Recheck oil level and top up accordingly. DO NOT overfill.
- Inspect spark plugs and change if required (torque: 17 ft-lbs or 1/4 turn after hand tightening).
- Add dielectric grease to coils to seal connections.
- Disconnect battery, clean and inspect and put on maintainer. More dielectric grease to keep m
- Tighten all clamps, check wires, etc.
- Lube up whole engine and jet nozzle area with XPS lube.
- Grease trailer wheels.
- Clean boat and wax.