That's deceptive, though. Aeordynamic forces usually increase as the cube of velocity, so while the fan may appear to be spinning fairly fast, it may be drawing virtually no power from the engine. The loudness of the fan is a better indicator- on my car the fan will roar quite loudly at fast idle, then go completely silent when the clutch disengages.... but the eye can't really see any difference in the speed of the fan.
Then the thermostat is BAD. The temp should never drop if the thermostat is doing its job. That's the whole point. What its probably doing is sticking open rather than closing smoothly as the temperature of the engine decreases. When the engine finally gets cold enough it will snap shut, but that's not how its really supposed to work.
I don't doubt that. But the problem is still the thermostat if the engine temperature falls below the normal operating temperature once its gotten up there in the first place.