If the radiator is clogged the fan clutch will not lock up as the heat doesn't pass through the radiator right. The clutch has a bi-metallic spring in it that "locks" it up. However they wear out just like everything else. Quick check for the radiator, get the engine hot, shut it off and feel across the center (the core) and check for even heating, if you find a cold spot, it's plugged.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.