well I have 72,000 miles on mine, and have never opened the radiator bottle or added any water either, like I said the fill bottle is where it should be with the coolant level that is.
I'm thinking either a clapsing hose or a thermostat sticking.
I looked at the radiator and it doesnt seem to have a blockage issue, but I may not know what I am looking for either. not many bugs there. also the trans cooler sits square in the middle of the grill.
would it help to flush the radiator?