The un-cooled coolant comes in at the top of the radiator- your warmest temp reading. Coolant is cooled as it travels down Radiator and into the water pump, then thru the distribution tube and block. It`s true that you should always run a thermostat as it promotes complete coolant flow to back of the block/head. If the block is clean and the radiator is absolutely flowing ok- then timing off/combustion gases leaking into coolant via leaking head gasket- super heating coolant/ faulty thermostat or wrong style- bypass housing, head gasket W /bypass hole wrong 1950-1951. Fan blade on backwards? Head milled too much-too fast of heat transfer/block bored too much-.080? Using Chinese gas?
Bob