I have a Mercruiser 140 hp straight 4 cylinder engine in a boat
which I want to keep in the lake and have available all year.
Usually it doesn't stay cold for long periods at a time here, but
this year it has been freezing or below for about a week or more.
I've kept the motor from freezing by using a handy little item
called a Thermo Cube:

http://tinyurl.com/yeg3jgl

and some lights, but wanted to winterize the motor for while
until things warm back up to normal. There is one drain cock on
the right side of the motor. I emptied that, and then dumped in
antifreeze at the top of the motor where the thermostat goes. I
left the cock open until antifreeze started coming out of it,
then closed it and continued filling with pure antifreeze until
it came to the top of the thermostat opening. That should mix
with whatever little water is left and keep the motor safe from
freezing at least down to zero degrees, right?

Also, I'm wondering if there is any reason to have a thermostat
on a boat that takes water in from the lake. Some people have
told me they are of no use, but others apparently put them in
since there is one in this boat. It is old and looks like it
probably doesn't work any more, and the spring has broken loose
from it. Would it be just as well to get rid of it and not use a
thermostat at all?