lot of BS in this thread...
Normally functioning viscous coupling fans are like this: (END OF DISCUSSION)
When they have not been in use for a while, they will be stiff. They turn with little effort, but wilol not spin freely.
When exercised either by yanking the fan back and forth by hand for awhile, or starting the cold engine and allowing to idle a few minutes, they will freewheel as if spinning loosely on a shaft.
When the clutch housing warms up, it will gradually increase the resistance to fan motion independent of the driven shaft in proportion to the temperature. An engine running above normal operating temperature just prior to shutdown will have a very stiff fan.
Under no circumstance should the fan exceed 80% of engine RPM at maximum throttle.