Data copied & pasted from other thread. Testing was done in summer in 70-90F ambients, as needed to ensure the clutch was or was not engaged, for testing purposes.


Car #2 - Bad Clutch:
With the engine at ~650rpm idle in park, pulley speed was ~810rpm, actual fan blade speed was ~275rpm (only ~35% lockup).
With the engine at 1500rpm idle in park, pulley speed was ~1900rpm, actual fan blade speed was ~500rpm (only ~25% lockup).
With the engine at 2500rpm idle in park, pulley speed was ~3200rpm, actual fan blade speed was ~500rpm (only ~15% lockup).
NOTE: The "bad clutch" test results were the same regardless of engine temp or ambient temp.


Car #3 - Good clutch, NOT engaged:
With the engine at ~650rpm idle in park, pulley speed was ~800rpm, actual fan blade speed was ~325rpm (~40% lockup).
With the engine at 1500rpm idle in park, pulley speed was ~1900rpm, actual fan blade speed was ~410rpm (~22% lockup).
With the engine at 2500rpm idle in park, pulley speed was ~3100rpm, actual fan blade speed was ~980rpm (~32% lockup).

Car #3 - Good clutch, engaged:
With the engine at ~650rpm idle in park, pulley speed was ~800rpm, actual fan blade speed was ~775rpm (97% lockup).
With the engine at 1500rpm idle in park, pulley speed was ~1900rpm, actual fan blade speed was ~1750rpm (92% lockup).
With the engine at 2500rpm idle in park, pulley speed was ~3200rpm, actual fan blade speed was ~2600rpm (81% lockup).


Conclusion: With a defective M119 fan clutch, the fan is spinning slower at freeway speeds than it does with a good (engaged/coupled) clutch at IDLE.