heat load created and requirenig dissipation at the radiator. I assume the 62 degree thermo temp you state is degrees C so that is about 144 F, well below the OEM thermo of 170F to start opening. So that would not be a cause for the overheat. Have you pressure checked the cooling system and also ckecked for CO gas in the coolant from leaky head gasket. What about any oil in coolant and/or coolant in the oil?
Have you done the radiator feel test I note in my post above?