The JD radiator fans move a lot of air. Enough to cool the block when the engine isn't running under a moderate to heavy load. This amount of air flow is meant to keep them cool during the summer months when brush cutting or other heavy loads. Ultimately you may need to block part of the radiator during the winter to keep the coolant temp up so you get good heat.
Would there be any benefit in flushing the cooling system and replacing fesh antifreeze/water mixture?