In water all winter
 

My son bought an old small house boat that he has to store in the water in Boston Harbor all winter. It has a merc I/O. I know outboards but not I/Os. How do you winterize an I/O that will stay in water all winter? Engine does not run. He is planning on getting it running and restored to live on next summer.
Thanks.

do you have shore power on the boat? Is the engine closed cooled?

if it doesn't run all you can really do is drain the water from the block and manifolds. Then fill them as best you can with non toxic antifreeze. If you can leave a droplight on in the engine compartment. the lightbulb will provide enough heat to keep things from freezing in case you missed any water in the block.