Do you winterize your own engine, or do you have the yard do it? I take the former approach, for three reasons. As my dad used to say, if you want to be sure a jobs done properly, do it yourself; Ive seen some pretty sketchy work done by so-called marine professionals over the years.
The second reason? It seems silly to pay someone to do a job thats a) not very time-consuming, b) not at all difficult and c) also happens to be pretty satisfying (to me, anyway).
Theres actually a third reason; by taking the time to perform these maintenance tasks yourself, you get a chance to really look over the innards of your boat in a way that doesnt happen during the sailing season.
You can carry winterization to illogical extremes, but when you pare it down to the bare essentials, your priorities should be engine, freshwater system and electrics. If you deal with those three before the first frost, then you can take your time with everything else.
If possible, Ill change the engine oil and filter before the boat is hauled. You need to run the engine for 20 minutes or so to get the oil nice and hot, and its hard to do that on land. If you have an oil discharge pump on your engine, I envy you. Otherwise, like me, youll probably use a suction pump with its pickup tube down the disptick hole. Hot oil is easy to suck up: cold oil isnt.
Ill place a disposable diaper under the oil filter and spin the filter off, or try to. Last year Id screwed the filter on too tightly and had the devils own job getting it off. I tried three different oil filter wrenches and they all slipped. Finally, I slipped a big hose clamp over the filter and tightened the bejeezus out of it; this gave the filter wrench something to bite on. I would love to install a remote oil filter, but Yanmar wants over $400 (!) for something that would cost $60 in an auto parts store.
Once Ive topped the engine off with new oil, Ill remove the hose from the engine cooling water seacock and place it in a bucket of antifreeze. Then Ill start the engine and run it for a minute or so until I see the antifreeze coming out the exhaust. A tarp under the exhaust through-hull catches the small amount of fluid that escapes. This clears the salt out of the raw-water passages and heat exchanger. I never do this job while the boat is in the water; that stuffs no good for the environment.
Once thats done, Ill remove the impeller, wrap it in plastic and place it where Ill be certain to find it in the spring. Finally, Ill spray the engine with a protective film of WD-40 and plug the air intake and exhaust through-hull with oily rags to keep moisture and critters out.