The text below is from the GM Service manual 4.3L V6 Engine
Water Pump Replacement (4.3L)
Drain the cooling system. Refer to Draining and Filling Cooling System .
Loosen the water pump pulley bolts.
Remove the cooling fan and clutch assembly.
J 46406 Fan Clutch Wrench
Remove the upper fan shroud.
Remove the fan clutch from the water pump in a counterclockwise direction using the J 46406 .
Remove the fan clutch assembly.
Remove the drive belt. Refer to Drive Belt Replacement Remove the water pump pulley mounting bolts.
Remove the water pump pulley.
Remove the radiator outlet hose clamp from the water pump.
Remove radiator outlet hose from the water pump.
Remove the water pump mounting bolts.
Remove the water pump from the engine.
Remove the water pump gaskets.
Clean the water pump gasket mating surfaces.
Install the water pump gaskets.
Install the water pump to the engine.
Apply a sealer (GM P/N 12346004) to the bolt threads.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque
and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Install the water pump mounting bolts.
Tighten the mounting bolts to 41 N·m (30 lb ft).
Install the radiator outlet hose to the water pump.
Install the water pump pulley.
Install the water pump pulley bolts.
Tighten the water pump pulley bolts to 25 N·m (18 lb ft).
Install the drive belt. Refer to Drive Belt Replacement in Engine Mechanical - 4.3L.
Install the fan clutch assembly.
Fill the radiator cooling system. Refer to Draining and Filling Cooling System .
Inspect the cooling system for leaks.