Roger Long wrote:
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?

I just discovered that our insurance policy doesn’t have a "haul by"
clause and I’d like to sail here in Maine as late as I can. With the
cooling system filled with salt water and the water temperature not
yet fallen, I can’t imagine that my 20 HP Yanmar is going to crack
something the first few nights the temperature drops into the high 20’s.
I’d sure hate to be wrong though.

When should I start worrying?

If there was an unseasonably cold night forecast, I'd probably go down
and warm up the engine just before bed.

I can't answer your exact question, but the last winter we headed
south we got overtaken by a nasty cold spell that we didn't expect.
If the forecast was for 28 degrees or less we drained the part of the
water system that runs through the cockpit; we had to do this 7 times
that December. The first time was in Myrtle Beach on Thanksgiving Eve
and the water lines on the dock burst.

We didn't worry about the engines because the water temp was still
fairly warm (in the 50's?) and I figured that would keep the engine
compartments from getting cold enough to freeze salt water.

There must be some type of safe heater you could use - even a 100 watt
bulb would add enough heat to prevent a freeze on a marginal night.
And, how hard is it to drain the water, or perhaps suck a quart of the
pink stuff into the engine?