Fan clutch - Please Help!

[Stocker]

Originally Posted by midnightrider78

I'm pretty sure the difference is the speed the fan is moving vs the water pump. I think I read somewhere that a standard fan clutch is moving at 70% of the drive(water pump) speed when its engaged and a heavy duty is 85%.

Per Hayden's website:

Standard Duty turns fan at 60-70% of shaft speed when engaged

Heavy Duty turns fan at 70-90% of shaft speed when engaged

Severe Duty turns fan at 80-90% of shaft speed when engaged