The radiator fan will turn all the time because it is driven by a belt off of the crankshaft. I would suggest getting a service manual and owners manual for the tractor to help you keep it running and fix any problems that might show up. Your tractor should have a thermostat in one of the radiator hoses. It might have been removed at some point in the past, if you have problems getting the tractor up to operating temperature, I would suggest checking and possibly replacing the thermostat.
Link to online parts catalog for Case VAC