The thermostat is located between the water outlet and a housing built into the intake manifold.
Disconnect the negative battery cable.
Remove the air inlet duct.
Drain the cooling system to a level below the thermostat.
Remove the thermostat outlet-to-engine retainers (usually either 2 bolts or 1 bolt and 1 stud), then remove outlet from the intake manifold.
Remove the thermostat from the housing, noting the orientation for installation purposes.
To install: Carefully clean the all traces of the old gasket or sealer from the housing and outlet.
Install the thermostat to the housing, oriented as noted during removal, then position a new gasket (if used).
Place a 1 / 8 in. Bead of RTV sealant in the groove on the water outlet sealing surface, then install the outlet while the sealer is still wet.
Install the outlet retainers and tighten to 21 ft. Lbs. (28 Nm) for the 4.3L 19-96 models or to 14 ft. Lbs. (19 Nm) for the 1997-99 models.
Properly fill the engine cooling system and check for leaks.
Install the air inlet duct.