I've since changed out the Derale 17117 with a factory fan blade from a late model Camaro. The 17117 wasn't pulling enough air through the radiator at idle. The Camaro fan is lighter (5-blade instead of 6 and the blades are aluminum), so I'm guessing the clutch is spinning it faster. Plus the new one has more pitch. Either way, I've got more airflow at low speeds, which is what I needed.
