I've run my 216 with and without a thermostat. Without it runs 110-170 degrees when it's 70-95 degrees air temp. That includes idling in long parades, sitting idling for up to an hour, or going down the road 50-55 mph. With a 160 thermostat it stays at 160 doing all of the above. I do have a six bladed fan on it. Even tho you have a new radiator it could still not function correctly. Also bad thermostat, not installed correctly, bad temp gauge, bad water pump, crimped radiator hose, engine timing, fuel mixture too lean, bad head gasket, clogged water jackets. I installed a new thermostat in the 216 and it heated to 212 real quick. Removed it and the engine ran cool. Ran it that way for years. I put the 160 thermostat in this spring.

1939 Chevrolet Stake Truck