I had a very hot 406 sbc, that ran a little hot. a mech. friend told me to take the 160 thermostat out and try a 180, guess what, it worked on the chevy. why ? I don`t know, other than keeping the coolant in the rad. longer.????
bingo.....you need to keep the coolant in the radiator long enough to cool it....If it doesn't stay in the radiator long enough, it doesn't matter what size radiator you have , how many cores, aluminum, etc.....