"I live in Cape Cod, MA and I
"I live in Cape Cod, MA and I just winterized my boat this past Sunday. We have had numerous nights well below freezing (as low as 18) and I did not have an issue. In my opinion it takes a deep, prolonged freeze to compromise your engine block. If your climate only has occasional nights / days below freezing I would use some common sense and judgement in regards to winterizing your boat. Oil coolers and fresh water sinks / tanks will freeze first so in anticipation of cold temps. drain these components. It is also very easy to drain the spitcocks on either side of your block, along with each manifold and the face of the raw water pump. Draining these items drastically decreases the odds of damage caused by freezing and takes very little time.
I run my boat in salt water and hold off from flushing the block with fresh water during cold months since salt water freezes at a lower temp. than fresh.
Keep in mind though, a few $5 gallons of antifreeze goes along way in comparison to replacing a cracked block. Good luck."