I have one on my car but never used it, even at -30* or so there'* no trouble starting the car.
But I have blown out 2 of them
On both occaisions I was tuning the car, at the time I was at WOT on the highway. It doesn't take long to loose most of the coolant in those situations, unfortunately there was so much coolant everywhere causing me to throw my 8 rib supercharger belt...in fact that was the first indication of trouble.
That said, the one in there now has gone through plently of abuse and a complete winter and still made it through.