Over cooling!

BTW, since your older A body likely does not have an overflow tank (it would not have had one new), then you cannot fill the rad to the top or it will indeed blow out some coolant every time when it gets hot. The FSM states that you have to leave the coolant fill in the rad about 1-1/4" below the lower edge of the rad cap opening in the top of the rad. That air gap inside the top of the rad HAS to be there for coolant expansion in a non-overflow system. Filling a non-overflow rad up to the top GURANTEES that it will blow out the excess coolant until a sufficiently sized air gap emerges in the top of the rad. I had that happen over and over when I first got my '62 Dart; I FINALLY read the FSM and learned to not fill the rad too high!

Man, I hope you get all the salt washed out form under your nice A body! We came back from Salem to Augusta County Sunday eve in that early snow fall towing a trailer; it was a bit nasty in places. People sure drive foolishly in small amounts of snow....