GM Full-Size Trucks 1988-1998 Repair Information

Thermostat

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REMOVAL & INSTALLATION



Gasoline Engines

See Figures 1, 2, 3, 4, 5, 6, 7 and 8


CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Drain the radiator until the coolant is below the thermostat level (below the level of the intake manifold).
  2.  
  3. Remove the water outlet elbow assembly from the engine. Remove the thermostat from the engine, or, on the 4.8L, from inside the adapter elbow.
  4.  

To install:
  1. Clean the gasket surfaces on the water outlet elbow and the intake manifold. Use a new gasket when installing the elbow to the manifold.
  2.  
  3. Install the new thermostat making sure the spring side is inserted into the engine, or, on the 4.8L, downward into the thermostat housing. Tighten the thermostat housing bolts to 20 ft. lbs. (28 Nm). On the 4.3L, 5.0L, 5.7L tighten the studs to 21 ft. lbs. (28 Nm). On the 7.4L tighten the bolts to 27 ft. lbs. (37 Nm).
  4.  
  5. Refill the cooling system. Start the engine and check for leaks.
  6.  



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Fig. Fig. 1: Remove the thermostat housing bolts



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Fig. Fig. 2: Remove the thermostat housing from the engine



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Fig. Fig. 3: Remove the thermostat from the housing



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Fig. Fig. 4: Thermostat housing-4.3L engines



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Fig. Fig. 5: Thermostat housing-4.8L engines



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Fig. Fig. 6: Thermostat housing-5.0L and 5.7L engines



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Fig. Fig. 7: Thermostat housing-7.4L engines, R/V series



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Fig. Fig. 8: Thermostat housing-7.4L engines C/K series

Diesel Engines
1988-95 models

See Figures 9 and 10

  1. Remove the upper fan shroud.
  2.  
  3. Drain the cooling system to a point below the thermostat.
  4.  



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Fig. Fig. 9: Thermostat housing-6.2L engines, R/V series



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Fig. Fig. 10: Thermostat housing-6.2L and 6.5L diesel engines-1988-95 C/K series

  1. Remove the engine oil dipstick tube brace and the oil fill brace.
  2.  
  3. Remove the upper radiator hose.
  4.  
  5. Remove the water outlet.
  6.  
  7. Remove the thermostat and gasket.
  8.  
  9. Installation is the reverse of removal.
  10.  
  11. Use a new gasket coated with sealer, Make sure that the spring end of the thermostat is in the engine. Tighten the bolts to 35 ft. lbs. (47 Nm) on 1988-91 models and 31 ft. lbs. (42 Nm) on 1992-95 models.
  12.  

1996-98 Models

See Figure 11

  1. Drain the cooling system to a point below the thermostat.
  2.  
  3. Disconnect the upper radiator (inlet) hose from the thermostat outlet.
  4.  
  5. Ufasten the thermostat housing bolt and stud, then remove the housing.
  6.  
  7. Remove the gasket and the thermostat.
  8.  
  9. Clean any remaining gasket from the thermostat hosing mating surfaces.
  10.  



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Fig. Fig. 11: Exploded view of the thermostat assembly components-1996-98 diesel engines

To install:
  1. Place the thermostat into position in the housing, then install the gasket.
  2.  
  3. Install the thermostat housing, the bolt and the stud. Tighten the bolt and stud to 31 ft. lbs. (42 Nm).
  4.  
  5. Attach the upper radiator (inlet) hose to the thermostat outlet.
  6.  
  7. Fill the cooling system.
  8.  
  9. Start the engine with the radiator cap still removed, until the upper radiator hose is hot (this means the thermostat is open).
  10.  
  11. With the engine idling, add coolant until the coolant level reaches the bottom of the filler neck.
  12.  
  13. Instal the radiator cap making sure the arrows line up with the overflow tube and check for coolant leaks.
  14.  

 
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