Probably this is something that you guys in the southern USA don't have to worry about, but its a fact of life here in Ontario and the northern States. The temperatures are just now beginning to dip below freezing at night, and its going to get a lot worse before it gets better. A cracked block or heads, and a sprung radiator are really nasty things.---and its so easy to forget to add anti-freeze. Probably everyone who lives in the "freeze" zone has experienced this at one time or other-----you build a new car, fill the rad with water for first firing (ya don't want anti-freeze in your oil---it does horrible things to bearings), and then it runs so good you forget to add anti-freeze. Or else you fill it up with good quality anti-freeze, and throughout the summer it boils over a bit in traffic, so you top the rad off with water when you get home----and keep on doing it untill you have diluted the anti-freeze untill it isn't effective any more.
Heads up guys---get out the anti-freeze and the big old funnel.