PackardDon wrote:
You must have a water distribution tube for proper cooling but your thermostat should be in the radiator. It opens and closes the grill bars to control the airflow through the radiator rather than on the water outlet controlling water flow. 1939 was the last year for that on junior models so perhaps your car was modified with a 1940 housing and thermostat.

Incidentally, I have a rebuilt 110 engine from an early 1940 but not sure if I have a spare water distribution tube.