The 496 doesn't have conventional block drains like other big blocks. It has a large allen plug on the port side of the block. If you pull it you will drain 3/4 of the antifreeze from the motor. The starboard side will still hold antifreeze. You do not drain the block for winterization, just check the antifreeze concentration and condition.

When I winterize my boat, I drain the motor with the air drain system, then pump 5 gallons of Marine antifreeze through the cooling system through the freshwater flush system. 5 gallons is way more than capacity, but antifreeze is cheap, boat parts ain't.

OEM Merc school and you will never find this info even in the OEM service manuals. The Gen III cool fuel system has to be drained 100 % - the 2006 and up 496 has the gen III cool fuel.

before draining anything on the engine and drive side - next is you have to run the engine for about 15 to 20 mins on your made up fuel supply.mix - the first fuel inlet fitting on the engine side - you connect your soup fuel mix to help all fuel system related components from corrosion and drying out.
Thats the internals of the fuel injectors, internals of the fuel rails, inwhich are GM junk as they corrode over time, and all fuel pumps as the corrode and can lock up from sitting and all fuel lines and all fuel cells. Do not run it on the MERC spec of 10 to 1 ratio of 2 stroke oil to gas. They are nuts with that. 50 to 60 to 1 ratio and you will be fine and a quality fuel stabilizer add in the mix as well.- then add about 100 to 120 to 1 and a quality fuel stabilizer to the boat fuel tank.

My boat is open cooled system,to winterize,I run antifreeze through it and take the blue drain plugs out and drain the block.not sure if original poster is open or closed.

all Merc 496 are closed cooling and Volvo Penta 496 is an option to have closed cooling or NOT. Volvo penta 496 comes either way. FYI to whomever

It does not matter the temp of were your boat sits for long periods - the fuel system has to be winterized and or laid up properly no matter what your app is - even carb engines and TBI engines are all done the same way nowadays or should say at least when I am laying up boats.

Next store your outdrive full down position. I do not think that was brought and there is 3 main reason why to do this. I try to never leave my outdrives stored up more than couple days anyways regardless what time of the year it is.

mine is 2007 is there more i need to be draining?

also i did add stabilizer to the fuel and put seafoam in the filter housing. but i didn't run any type of 2 stroke oil through it. should i pull it back out and do that? (thats going to suck if i do it was a pain in the butt to get in there.) but my boat is worth the time. also the drive is down. i always leave my drive down unless in use or being towed.

im not looking to drain the antifreeze. and not needing to run antifreeze through the raw water side as its staying indoors over the winter. i just want to make sure that i drained all of the water from the manifolds so its not sitting in there all winter.

also keep in mind im in MD so my boat will probably be pulled out of storage towards the end of march and started to get ready for the season.

GEN III cool fuel needs to completely drain of all water and complete fuel system laid up properly. Can not be more to a T about it in my posts. Granted i have winterized boats till the cows come home especially when the gettin was good in the boat biz but those days are gone. Youtube and bilge heats and forums killed winterization for all marine shops. Just saying

so that is over 90 days - did you take fuel samples to make sure no water was in the fuel and fuel tank ? Did you check for water in the GEN III cool fuel basket as that is what its job is suppose to do.

there is alot more to winterizing a boat than draining the block or running it on anti freeze - did you grease your gimbal bearing ? Did make sure the tiny water holes / drain holes in the outdrive were not block so they drained as well and make sure your speedo hole is not block holding water ? .

did you make sure there was no water in the outdrive gear oil and it is always best to change all oils and filters for lay up. Does your gas cap have a good o-ring seal on it so helps against condensation ? Did your heat exchanger completely drain all of its water ? - I would not just count on the air actuator system / pump. They work good for nice new clean engines but get a bunch of scale or sand in the raw water side of all this and they do not drain very well. Good luck and I pretty much covered most of it for how it should be done per the OEM .