They have resistance even at room temperature. As the silicone fluid in the fan clutch heats up, the resistance becomes greater making the fan spin faster with less slippage in the clutch. At full lock, they are still only spinning at about 90% of engine speed according to Hayden's web site.
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount98 Dodge Cummins 24 Valve