I did find this one...
Melissa,
I have a somewhat more conservative approach - maybe because I'm further north and it can get to 40-50 below where my boat is wintered. And this is probably after the fact, but for the record:
I would not use RV, potable water system antifreeze. I use the propylene glycol-based, (more eco-friendly) antifreeze meant for engine coolant and storage. It has corrosion inhibitors and is meant to be diluted to a desired protection temperature. You can't go by color - there are reds, greens and blues that are available. Make sure it is not the common auto antifreeze which is ethylene glcol-based.
As Loren says, there are two ways to winterize and although the original engine manual prescribes complete draining, many now suggest it is better to leave the engine full of antifreeze to reduce corrosion. The engine antifreeze also seems to be slightly lubricating to the water pump impeller blades.
I adjust my antifreeze mixture first, so I want to get out as much water as possible to prevent any additional dilution. Most of the water comes out when the rear drain tube is opened. This is the one back near the water pump. Even more water comes out there when the forward plug is removed - it evidently provides a venting action. I also remove the plugs on the manifold side, but very little water ever exits there.
I have winterized without removing the thermostat, but I do now because it makes me at least feel like the antifreeze is getting in there more freely and it also gives me a yearly look inside the cooling system. If there is some crud visible or feelable, it might be time to flush next season. If you do remove it, remember the two nuts holding it on are also acting as head bolts, so should be torqued to 35 ft-lbs if you intend to run the engine with it removed. I do run it with the t'stat removed and a clamp on the bypass hose when I draw in the antifreeze. As soon as some antifreeze comes out the exhaust, I spray fogging oil into the carb until the engine dies. I remove the spark plugs and add more fogging oil to each cylinder and manually crank the engine a couple of revolutions to distribute it before replacing the plugs.
I cover all openings (breather, carb, etc.) with aluminized plastic to keep any moisture out. I also plug the exhaust fitting on the transom. (Some people cover the distributor and loosen the alternator belt, but I have not done that.)
You don't say what type of muffler you have, but if it is the old standpipe style, I would try to drain that too. Sometimes access is difficult and I winterized several years without doing this so it may be overkill. (When I had a new standpipe made, I put an extra fitting at the bottom for draining - but then I also made a large cut-out in my quarterberth so I can get at it.)
If you have winterized with RV antifreeze, I would recommend testing the mixture now in the block. You will need an antifreeze tester specifically made for propylene glycol. If the -50 RV stuff is diluted even a small amount, it can really affect the protection temperature.
If you leave the engine intake valve closed as suggested above, make sure you have allowed it to drain first after hauling. I made that mistake once and had to replace the freeze-cracked valve in the spring in my slip by pulling the mast over until the intake was above the waterline. I just leave it open now.
This looks like it is from someone in my same neck of the woods as well (Walter Pearson), so that is a good thing. If he hadn't sold the boat in 2012 I could go meet him as I intend on sailing to that part of the lake next summer.
