GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual

Thermostat

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DIAGNOSIS



Make an operational check of the thermostat by hanging the it on a hook in a pot of warm water. Insert a thermometer into the water (neither the thermostat or thermometer should touch the metal sides or bottom of the pot) and heat the water to the thermostat opening temperature (stamped on the top of the thermostat). With the temperature within 10° of the opening temperature, the thermostat should open. If not, replace the thermostat.

REMOVAL & INSTALLATION



See Figures 1 through 8

1.9L Engine
  1. Drain the cooling system to a level below the thermostat.
  2.  
  3. Disconnect the PCV hose, the ECS hose, the AIR hose and the TCA hose.
  4.  
  5. Remove the air cleaner-to-carburetor retainer(s) and loosen the clamp bolts, then lift the air cleaner and disconnect the TCA hose from the thermosensor (on the intake manifold). Remove the hoses from the air cleaner-to-carburetor slow actuator and the air cleaner-to-vacuum control (California), then remove the air cleaner assembly.
  6.  
  7. Remove the outlet pipe-to-inlet manifold bolts, the outlet pipe (with the radiator hose attached) and the thermostat from the engine.
  8.  
  9. Using a putty knife, clean the gasket mounting surfaces.
  10.  
  11. Installation is the reverse of removal. Use a new gasket and apply a thin coat of sealant to both surfaces of the gasket. Torque the outlet pipe-to-intake manifold bolts to 21 ft. lbs. (28 Nm).
  12.  
  13. Properly refill the engine cooling system, then start the engine and check for leaks.
  14.  



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Fig. Fig. 1: When draining coolant, remember to use a funnel in order to prevent a mess



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Fig. Fig. 2: Loosen and remove the water outlet retainers



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Fig. Fig. 3: Lift the outlet away from the thermostat and housing with the hose still attached



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Fig. Fig. 4: Remove the old thermostat from the housing



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Fig. Fig. 5: Be sure to clean the housing and outlet of all traces of old gasket/sealant



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Fig. Fig. 6: Install the new thermostat to the housing



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Fig. Fig. 7: For most vehicles covered by this manual, apply a thin coat of sealant to the outlet groove



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Fig. Fig. 8: Install and tighten the bolts; using a torque wrench if a specification is given

2.0L Engine

See Figure 9

The thermostat is connected to the water outlet and the thermostat housing, located at the top front-side of the engine.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system to a level below the thermostat.
  4.  
  5. Remove the steel vacuum tubes.
  6.  
  7. Remove the water outlet-to-thermostat housing bolts, then lift the outlet from the thermostat housing and remove the thermostat.
  8.  

To install:
  1. Using a putty knife, clean the gasket mounting surfaces.
  2.  
  3. Place an 1 / 8 in. bead of RTV sealant on the water outlet. Place the thermostat, with the power element down, in the housing and install water outlet while the RTV is still wet.
  4.  
  5. Torque the water outlet-to-thermostat housing bolts to 15-22 ft. lbs. (20-30 Nm).
  6.  
  7. Install the steel vacuum tubes, then connect the negative battery cable.
  8.  
  9. Properly refill the engine cooling system, then check for leaks.
  10.  



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Fig. Fig. 9: Thermostat location and mounting-2.0L engine

2.2L Diesel Engine

The thermostat is connected to the water outlet and the thermostat housing, located at the top front-side of the engine.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system to a level below the thermostat.
  4.  
  5. Tag and disengage the electrical wiring.
  6.  
  7. Remove the water outlet-to-thermostat housing bolts, then lift the outlet from the thermostat housing and remove the thermostat.
  8.  
  9. Using a putty knife, clean the gasket mounting surfaces.
  10.  
  11. Installation is the reverse of removal. Using a new gasket and sealant. Apply a thin coat of sealant to both sides of the gasket, then install the water outlet while the sealant is wet. Torque the water outlet-to-thermostat housing bolts to 10-17 ft. lbs. (14-23 Nm).
  12.  
  13. Properly refill the engine cooling system, then check for leaks.
  14.  

2.5L Engine

See Figure 10

The thermostat is located inside a housing attached to the front of the cylinder head.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system to a level below the thermostat.
  4.  
  5. Remove the thermostat outlet-to-engine retainers, then remove outlet and the thermostat.
  6.  

To install:
  1. Using a putty knife, clean the gasket mounting surfaces.
  2.  
  3. Using RTV sealant or equivalent, place an 1 / 8 in. bead of sealant in the groove of the water outlet.
  4.  
  5. Installation is the reverse of removal, install the housing while the sealant is still wet.
  6.  
  7. Torque the thermostat housing-to-engine bolts to 18-20 ft. lbs. (24-27 Nm).
  8.  
  9. Refill the cooling system and check for leaks.
  10.  



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Fig. Fig. 10: Thermostat location and mounting-2.5L and 2.8L engines

2.8L and 4.3L Engine

See Figures 10 and 11

The thermostat is located between the water outlet and a housing built into the intake manifold.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system to a level below the thermostat.
  4.  
  5. Remove the thermostat outlet-to-engine retainers (usually either 2 bolts or 1 bolt and 1 stud), then remove outlet from the intake manifold.
  6.  



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Fig. Fig. 11: Thermostat location and mounting-4.3L (VIN Z) engine; the VIN W engine is similar

  1. Remove the thermostat from the housing, noting the orientation for installation purposes.
  2.  

To install:
  1. Carefully clean the all traces of the old gasket or sealer from the housing and outlet.
  2.  
  3. Install the thermostat to the housing, oriented as noted during removal, then position a new gasket (if used).
  4.  
  5. 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.
  6.  
  7. Install the outlet retainers and tighten to 21 ft. lbs. (28 Nm) for the 2.8L and 4.3L (VIN Z) engine or to 14 ft. lbs. (19 Nm) for the 4.3L (VIN W) engine.
  8.  
  9. Properly fill the engine cooling system and check for leaks.
  10.  

 
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