I was wondering, does the coolant have any place to go if it freezes? Thats what happened to my block (-23 F wind chill this morning), I got it thawed out but it leaks badly near #1 cylinder somewhere near the middle or bottom of the block. I think its leaking out the water pump but not sure. I was wondering about this because a long time ago I had a Ford F-100 with a 390, and that motor had "expansion plugs" that would pop out if the coolant froze...

 

Could have been the freeze plugs........holes left in block when cast to remove sand, then plugged later.