The entire situation with the fan clutch leaves me with questions.

Dave has stated that the clutch won't "engage" until it sees 100C. But, if this were true, a brand new clutch and radiator would allow the engine temp to climb to well over 100C. until the clutch "engaged".

Personally, I don't believe that it "engages" similar to a step function at a given temperature. It probably happens more gradually, beginning at a temp. of 85C. and finishing (fully coupled) at a temp. of 110C. These figures are just a guess.

With restricted airflow, the temperature at the fan would likely be hotter than with full airflow. The reduced quantity and velocity of the air will be warmed to a higher temperature and thereby cause the fan to engage sooner. This would be a desirable result of a partially clogged radiator.