I have F225's, I agree with all above.
1- I put fuel stabilizer in my tank and star-tron(if the ethanol breaks down this absorbs it and lets it pass through the engine safely), then fill my tanks, this way it mixes better instead of sitting on top. I'd fill the tank rather then leave it empty, close to full leaves little room for condensation, but it can still form because of the ethanol, leaving it empty puts more air in the tank and having a tank sit with air in it can cause problems and quicker deterioration, this also speeds up the break down of ethanol.
2-I change my oil and oil filter, even if it was changed at 100 hours during the season, to me it is preventive maintenance and also will allow me more time next season to run the boat before having to do the change, plus it is much easier and safer/cleaner to do it out of the water. When putting new filters on, coat them with 4 stroke oil, do not install dry.
3- I then change my lower unit oil, I pull the boat every 100 hours to change it during the year, but I will change it while it is out to get the full 100 hours next season, I'd rather change it too soon then leave it in too long, that is bad for the lower unit. It is also good to check the color and quality of the lower unit oil at the end of the season, that way if there is a problem you have the time of your lay up to have it attended to and fixed. When putting the screws back in, install new gaskets, do NOT use the old one, they break down and will let water in and damage the lower unit over time.
4- Lastly,I do the engines in case the engine needs service, no point in winterizing it then changing fluids and finding something wrong. I run the engines, about 5 or so min each with the ear muffs on, this flushes the engine well and gets stabilizer into the engine. Then, pull each plug and spray fog oil into each cylinder, I usually turn key over quickly after each cylinder is sprayed with plug out, this is how my mechanic taught me, most say it does not matter much.
I did my carbed engines for 10 years this way, my HPDI for 8 and the F225's for 2 years and never had an issue with winter lay up.
5- Once this is done, trim the engines and if you can, put cinder blocks under the drives and a piece of wood over top, and lower to put some of the weight on them and off transom.
6-Hit all fittings with grease.
7- Remove batteries, coat all terminals in vasaline(you can sue grease also but I've found the vasaline lasts longer), easy cleaning off in spring and will keep the terminals from corroding. Make the terminals so you know how to reconnect them.
8-Store batteries inside, not on cement. Over the winter, trickle charge them from time to time, if they are over 3 years old, consider getting new ones or at a minimum. If you plan to keep them or think they are fine, have them load tested at a local mechanic.
9- Remove props and grease hub and shaft.
I agree with Brad1, do the maintenance in the fall, that way your engines are ready to go in the spring, and if service or repairs are needed, they can be done ahead of time when your local mechanic is not packed and has time.
In the spring I run the motors with ear muffs for 15 min after I put the props and batteries back on. I change my zincs if needed and you should be set. I typically recheck my oil level to be certain it is enough. I also change my fuel/water separator filters, no sense in doing it in the fall, they will sit with fuel and it WILL break down in them and gather water.
After a few trips, maybe 5 hours, I change my plugs. I swear they never are the same after the fogging oil runs through them. I wait a few hours before changing them so the old plugs can pass most of it through, fogging oil can foul a plug from time to time(I've never had it happen but have heard other boaters have it happen), I keep my new set on board in case it is ever needed. Once my 5 hours are reached, new plugs go in and I'm set for the year or atleast 100 hours.
