Starting a BB Duster project

The test I ran was to start the engine cold and put a thermometer in the radiator while the engine was warming up. With my old thermostat the water in the radiator was the same temp as the engine temp. With the new thermostat the water in the radiator stays cold until the engine gets to about 170 and then a little bit of warm water starts to circulate into the radiator. Once I did that test it was obvious that my thermostat wasn't working properly even though it appeared to work fine when I tested it in a jar of hot water.