Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
There is actually a special tool that will hold everything from turning when you take the fan off. Here is what the book says to do. The threads are left handed so you would go in the opposite direction than you normally would.
Caution: Left-hand threads. Using special tool 11 5 050 brace against pulley and unfasten cap nut from water pump using special tool 11 5 040. Remove fan wheel with fan coupling from water pump.
Installation: Tighten down fan wheel using special tool 11 5 040. Tightening Torque, refer to Engine, Specifications.Note: When using special tool 11 5 040, 30 Nm on the torque wrench scale are equivalent to a tightening torque of 40 Nm.
Unfasten screws and detach fan from fan coupling.
ASE Certified Technician
ASE Master, 30+ years exp. former shop owner, diagnostics, driveability tech