GM Full-Size Trucks 1970-1979 Repair Guide




See Figures 1, 2, 3 and 4

Click image to see an enlarged view

Fig. Fig. 1: Use a ratchet and socket combination to unfasten the water outlet elbow bolts

Click image to see an enlarged view

Fig. Fig. 2: Remove the water outlet elbow housing

Click image to see an enlarged view

Fig. Fig. 3: If equipped, remove and discard the thermostat-to-elbow gasket

Click image to see an enlarged view

Fig. Fig. 4: Remove the thermostat by simply lifting it out of the housing

  1. Disconnect the negative battery cable.
  3. Properly drain the radiator until the level is below the thermostat level (below the level of the intake manifold).

When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Unfasten the water outlet elbow retaining bolts, then remove the water outlet elbow assembly from the engine.
  3. Remove the gasket.
  5. Remove the thermostat from inside the elbow. Thoroughly clean the gasket mating surfaces.

To install:
  1. Install new thermostat in the reverse order of removal, making sure the spring side is inserted into the elbow. Clean the gasket surfaces on the water outlet elbow and the intake manifold. Use a new gasket when installing the elbow to the manifold. On later models the thermostat housing may have been sealed with RTV sealant. If so, place a 1 / 8 in. bead of RTV sealer all around the thermostat housing sealing surface on the intake manifold and install the housing while it is still wet. Refill the radiator to approximately 2 1 / 2 in. below the filler neck.

If the thermostat is equipped with a pin hole, be sure to install pin side facing upwards.