been in the 90's here a few times and lot of mid to upper 80's. Only thing I have done is a 180 T-Stat and the chip. The car only saw over 200 once and that was at the track.
I use some water wetter every now and then and def some coolant in the winter. I flush out my radiator and put in fresh water every 2 weeks or so. I just look into the radiator now and then and if I see anything on the cap I usually flush it then also. Sometimes a rusty red looking muck appears there.