Has a Bi-Metallic spring operating system that allows the Fluid to move into
another chamber inside the clutch (Thereby "Locking" the "Clutch") once a
certain preset temperature airflow from the Condenser/Radiator is "sensed"
by the Bi-Metallic Strip.

The "Clutch" does not really "Lock up",when operational it CAN be stopped by
a Foreign Object. A.K.A. "Noodleheads" Body Parts would fit the bill.
Yow! that did hurt.

The Fan Clutch's Optimal Operating Parameters are at engine operating temperatures.
The Fan Clutch will disengage above a certain RPM range.

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'84 300SD sold
124.128