GM Bonneville/Eighty Eight/LeSabre 1986-1999

Thermostat

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The thermostat is used to control the flow of engine coolant. When the engine is cold, the thermostat is closed to prevent coolant from circulating through the engine. As the engine begins to warm up, the thermostat opens to allow the coolant to flow through the radiator and cool the engine to its normal operating temperature. Fuel economy and engine durability is increased when operated at normal operating temperature.

REMOVAL & INSTALLATION



See Figures 1 through 10


CAUTION
Never open, service or drain the radiator or cooling system when hot; the system is under pressure and will release scalding hot coolant and steam which can cause severe burns and other bodily harm. 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. If necessary, unfasten the retainer and remove the upper engine cover.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Remove the air cleaner and duct assembly.
  6.  
  7. Partially drain the engine cooling system, into a suitable container, to a level below the thermostat.
  8.  
  9. Disconnect the upper radiator hose from the water outlet.
  10.  



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Fig. Fig. 1: Unfasten the hose clamp, then disconnect the radiator hose from the water outlet

  1. If necessary, detach the electrical connections from the throttle body assembly.
  2.  
  3. Unfasten the water outlet attaching bolts, then remove the water outlet.
  4.  



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Fig. Fig. 2: Remove the water outlet attaching bolt (see arrow) ...



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Fig. Fig. 3: ... then remove the water outlet for access to the thermostat

  1. Remove the thermostat. Remove and discard the gasket.
  2.  



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



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Fig. Fig. 5: Remove and inspect the top O-ring (1) from the water outlet (2) ...



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Fig. Fig. 6: ...and do the same with the lower O-ring

  1. Thoroughly clean the manifold water inlet and water outlet mating surfaces. Inspect the water outlet for corrosion or other damage, and replace if necessary.
  2.  



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Fig. Fig. 7: A water outlet that is badly corroded, such as this one, should be replaced



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Fig. Fig. 8: Exploded view of the thermostat and housing assembly - 3.8L (VIN C) engine



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Fig. Fig. 9: Thermostat and water outlet mounting - 3.8L (VIN L) engine shown



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Fig. Fig. 10: Exploded view of the thermostat, gasket and housing assembly - 1997 vehicle shown

To install:
  1. Position the thermostat into the intake manifold with a new gasket.
  2.  
  3. Install the water outlet to the intake manifold with RTV sealer. Tighten the attaching bolts to 20 ft. lbs. (27 Nm).
  4.  
  5. Connect the radiator hose to the water outlet housing.
  6.  
  7. If necessary, attach the electrical connections to the throttle body assembly.
  8.  
  9. Install the air cleaner assembly, then connect the negative battery cable.
  10.  
  11. Refill the engine with the specified type and amount of engine coolant. Start the engine and check for coolant leaks.
  12.  

 
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