The water pump on your Chevy Trailblazer circulates engine coolant between the engine and radiator, and is one of the components powered by the drive belt. If the pump is damaged, leaking or not working in any way, the vehicle is likely to overheat. The pump replacement process for a 2003 model is the same regardless if your model has the 4.2- or 4.3-liter V-6 engine or the 5.3-liter V-8.
Make sure the engine is cool before you begin working. Disconnect the battery's negative cable using a wrench on the cable clamp nut.
Place a large container under the radiator, remove the radiator cap and detach the lower radiator hose by loosening its clamp with pliers. Pour the engine coolant into the container through the hose.
Loosen the clamps for the fan duct and resonator and disconnect the air temperature sensor connector, disconnect the fuel pressure vacuum line and remove the resonator's mounting bolts.
Unbolt and remove the air intake baffle from the radiator support. Disconnect the upper radiator hose and electrical connectors. Turn the fan clutch hub counterclockwise to remove it from the pump and then unclip and remove the shroud.
Rotate the drive belt's tensioner pulley clockwise with the wrench and slip the serpentine belt off the pulleys. Make sure you know the exact path the belt is routed on the pulleys.
Hold the water pump pulley in place with a strap wrench and remove the pulley's four bolts with a wrench. Remove the pulley.
Unscrew the water pump's five mounting bolts with the flare-nut wrench and remove the pump; if the pump is stuck, tap it with a soft-faced hammer.
Clean all traces of the gasket material from the engine block using a rag soaked in acetone or lacquer thinner
Apply a thin coating of RTV sealant to both sides of a new gasket and install it on the replacement water pump.
Position the water pump on the engine and apply the bolts, making sure the pump gasket stays in position. If you have a torque wrench, tighten the bolts to 89 inch-pounds. Install the pulley and tighten its bolts to 18 foot-pounds.
Re-install the drive belt by loosening the tensioner and slipping the belt onto the pulleys.
Install the radiator shroud, fan clutch assembly and the air intake duct and resonator in the reverse order of removal. Reconnect the negative battery cable.
Fill the radiator with engine coolant at the radiator filler neck, using a fresh half-and-half mix of water and antifreeze if the old coolant is contaminated.
