Sorry but 'drying' a cast iron engine will greatly shorten the service
life. What happens is that the cast iron begins to form 'slab rust'
..... huge plateletts of ferric rust that propagates between the natural
'laps' of the casting. Cast iron, due to the way it cools when molded
is similar to an 'onion' ... and the ferric corrosion (usual severe
rust) will rapidly develop between the 'laps' and form ferric rust ,
develop extreme pressure between the natural 'laps' and begin to
destroy the casting. If you keep the engine 'wet' (using such things
as antifreeze with rust inhibiters0 this process is greatly retarded.
Cast iron is a good metal vs. sea water as the high operating
temperature produces 'ferrous' rust ... a blue/black oxide that
actually protects against ferric rust.

The moral of this story is dont 'air-dry' your engine by draining all
the water out ..... put in a mixture of water and antifreeze - and
this will keep the protective 'ferrous' layer intact. Otherwise,
expect to develop pin holes and leaks in short order.

hope this helps.

In article , Steve
wrote:

"Roger Long" wrote in message
...
Can anyone out there give me some informed and real world (yeah, I know
this is a newsgroup but, hope springs eternal) insight as to how
vulnerable raw water cooled engines are to damage from freezing?


My Volvo is designed for sea water cooling and each cylinder jacket,
manifold and the OEM "water lift muffler" has a drain cock. Seems like a lot
to remember each fall but these drain every drop of water from the block. To
prevent these cast iron surfaces from rusting over the winter, I have
three-way sea cock that allows me to pump anti freeze into the system. I
don't actually do this, here in PacNW, since the temp never get that cold in
my boat (heater) and I like to have the option to go out for you sail when
the winter weather is nice.

Check the location of your drain cocks on you Yanmar, see if they drain all
the lowest points.

I happen to have a small Volvo MD7A here with a cracked exhaust manifold
because this model didn't have a drain cock and it must have frozen the
standing water. Such a drain cock would have saved this nice little engine.

Now I'm rambling. Sorry.

Steve
s/v Good Intentions