Sounds to me as if you are overheating. If you boiling in the overflow thats hot. The sides are called tanks. If you cracked the tanks, was your coolant ratio off? Its been pretty cold, too much water in the system can do that to you.
Drop a new rad in, flush it, fill it with some good stuff, top it off with some 40 below and run the piss out of it like you intended to do.
Good Luck.