I've been using water over the summer because my waterpump has been broke for a while. It was cold the other day and the water froze and would not start (of coarse). It defrosted for now and starts up, but now overheat due to a leak that spills from under the engine. Hopefully it is a freeze plug and not my engine cracked.

yes with any luck its just a core plug pushed out by the ice..the pump leaks throw a bearing weep hole telling you its on its way out.now if u dont fix it,and its part of the timing belt then it will totally wreck the engine and head..