[Kager67]

I would say you have 50/50 chance. The radiator will freeze first because there is alot less steel insulating it. It depends on how cold it actually got. I have seen blocks with pure water in them not break, down to 20 degrees or so. I will also say along with the other guys, never use only water in an engine, I have seen "freeze" plugs rust so bad they had pin holes in them(you can imagine what the rest of the motor looked like inside). Antifreeze not only transfers heat better than water, it is also a lubricant for your cooling system. Good luck.

Kage