I would change the oil and filter, then run it for a few minutes. You don’t want used oil and condensation sitting in there all winter. Don’t run the boat out of the water, unless you have a way to supply water to the outdrive. The water pumps will burn up fast when ran dry. You can fog the motor like someone mentioned, or pull the plugs and squirt a teaspoon of 20w oil in cylinders and crank it over a few times without the plugs. Then wipe up any oil and put the plugs back in.
I have a couple 454 mercs. I pull the hoses off the back of the rawwater pumps, hoses on the back of the oil coolers, the hoses on the bottom of the water pump on the block (looks like the ones a car has) then the hoses from the bottom of the exhaust manifolds. All I use for this is a socket driver. You can use a screwdriver, but it takes a lot more time. Sometimes the hoses are pain to get off.
Then I open the petcock valves on each side of the block. I would take them all the way out, then run a piece of wire into the openings to check for any blockage. Rust will block them sometimes. Some exhaust manifold will have petnoodles on the bottom of them too. I also have water pressure gauges, so there is a 1/4" hose going into the side of the block that has to be removed.
Tools needed
Socket driver.
Pliers to open the pitaxles, if they are stuck.
Piece of wire
Spark plug wrench
Oil filter wrench
You can leave it this way for the winter and put all the parts in a plastic bag and leave it on top of the motor.
I know some people will hook everything back up, pull the thermostat housing off and pour antifreeze in till it runs out the drive. They make special environmentally safe antifreeze for boats.
Every setup is a little different, so get the book.
Rash
