Already time for a cooling system rebuild.

Chris Nicholson said
He suggested doing a Prestone flush before taking anything apart, to make sure it doesn't have decades of gunk built up.

not saying it will definitely happen, but i'm guessing your going to find a rotted freeze plug or two after stirring up all the crap that's probably in the motor. when i get a "new" mopar i like to pull the motor, pull the water pump, knock out the freeze plugs out and clean the crap out of it. sooner or later, you will