On the merc website they have a video highlighting the 496 HO. The guy just hooks up the little pump, gives it about 10 strokes, and claims that all the water is drained. How realistic is that? I know people run AF through to be sure. I want to start doing some testing on warm days but I know there is about 6-8 more weeks of cold in MD.

With my old motor, late or early in the season I would just pull the hoses off the manifolds and the blue plugs out of the block. I never had a problem.

I hooked an air compressor up to mine, and pulled out the (5) blue plastic freeze plugs. I then proceeded to pull the entire water pump assembly off to install fresh water flush kits (total b.itch by the way). Both hoses still had water and so did the water pump. Its not a 100% perfect system, and some of the pressure valves can go bad as well. Safest bet is a bilge heater or A/F in event of deep freeze.

The video will tell you the air system is to extend a boaters season, if there is any chance of a hard freeze you should winterize.
Bryan

I'll tell you a little story about quick winterizing - when I bought my first IO (had an O/B, which is MUCH easier to winterize), I was told by a couple of people that all you have to do is buy a couple gallons of antifreeze, get engine to operating temp, put hose in antifreeze and run the stuff through the block w/engine running (engine sucks the antifreeze up and into block). I was told to shut it off when you see antifreeze blowing out the exhaust. What they DON'T tell you is that, after you get the engine to operating temp, you have to shut off to remove the hose from the spigot and connect it the source of A/F. When I did that (must have been real cold), the thermostat must have closed, because no A/F went into the block. I noticed some pink stuff leaking out the water pick-ups of the drive, and (luckily) I investigated. Removed the cover and saw icicles hanging from the hoses! I bought a space heater at West Marine and cranked it. I lucked out, no damage.

Bottom line and lesson I learned, there is no easy way to do this - remove the hoses and blue plugs and do it right.

After this episode, I read the manual - the 454 holds about 5 or 6 gallons of liquid - two gallons was a total joke!

Good luck (although a little late now to be winterizing, isn't it?

The heat exchanger will tend to hold water after pressurization....I ran RVAF thru mine this year and then pressurized it...Removed blue plugs and heat exchanger end caps..