A fan clutch wrench set is a pair of flat, thin steel wrenches used on trucks and rear-wheel-drive vehicles. The engine cooling fan is bolted to the water pump pulley using a thermostatic fan clutch. Loosening this connection is difficult because the water pump shaft spins freely. The fan clutch kit solves this by using one wide, open wrench to slip over the water pump pulley bolts to hold it steady, while a second wrench turns the large nut on the fan clutch housing.
Because these nuts are exposed to road water and engine heat, they often rust solid. They are also subject to rotation forces, meaning many have left-handed threads. Always check the fan shroud sticker or service manual to see which way to turn the nut. If the nut is seized, you can use a pneumatic fan clutch wrench that attaches to an air hammer. The rapid hammer vibrations pop the nut loose instantly.