I take it you refer to the surface rust. When it was acid washed and rodded out, he asked me if I wanted it painted, I was in a hurry, said, no, I'll handle that. My bad. Paint is off a lot of the brass as well. Paint really isn't going to fix this (despite what the theoretical physics says about black and heat transfer)? And isn't radiator paint "special" (thinner than regular, plus heat rated)?

 

I have no idea about radiator paint.