Just installed mechanical temp. gauge last week on my 66 C-code/Auto with factory A/C. Car has shroud and 5 bladed fan. Radiator is 3 yrs. old car has coolant recovery and 50/50 coolant mix. Thermostat is 180 deg. So after driving a(A/C off) few miles once warmed up it ran from 200- 205 deg then at signal 210-215 degrees. Stopped and checked temps with my infrared temp. gun,results: At thermo. housing at idle= 200-205 top of radiator= 205 Upper hose( middle)= 180 and lower hose= 150 degrees. I touched each hose(engine off) and lower one was cooler,hot top real hot. Is the temp. differantial normal from lower to upper? It seems to me once thermostat opens they would be closer in temps. BTW - Thermostat bypass temp.= 190 degrees. I guess if thermostat was not opening bypass would not have volume to cool motor and it would be running hotter then 200-210 aver.? Also motor is bored 60 thou. over and could be a contributor? Thanks all for your help,sorry for the novel. I never gave it muck thought till I bought Temp. gauge.LOL