Chrysler Full-Size Trucks 1989-1996 Repair Guide

Thermostat

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REMOVAL & INSTALLATION



Gasoline Engines

See Figures 1, 2, 3, 4 and 5

The thermostat on all gasoline-powered vehicles is located beneath the thermostat housing at the front of the intake manifold.

  1. Drain the cooling system to below the level of the thermostat.
  2.  


CAUTION
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.



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Fig. Fig. 1: Exploded view of the thermostat installation-V6 and V8 engines

  1. For 1994-96 V6 and V8 models equipped with air conditioning:
    1. Remove the support bracket (rod) located near the rear of the alternator.
    2.  
    3. Remove the drive belt.
    4.  
    5. Partially remove the alternator by removing the necessary alternator bolts. If equipped with 4WD, unplug the 4WD indicator lamp harness (at the rear of the unit).
    6.  
    7. Remove the alternator. Position it to gain access for thermostat gasket removal.
    8.  

  2.  
  3. On V10 engines, remove the two support rod mounting bolts and remove the support rod (intake manifold-to-alternator mount).
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Fig. Fig. 2: Remove the thermostat from its housing



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Fig. Fig. 3: Clean away all remaining gasket material and old sealer, if any, to ensure a tight fit upon installation

  1. All models: Remove the upper radiator hose from the thermostat housing. Note the positioning of the thermostat. It is important that the thermostat is correctly installed.
  2.  



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Fig. Fig. 4: Exploded view of the thermostat and water box-2.5L engine

  1. Withdraw the housing bolts and remove the housing and the thermostat.
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Fig. Fig. 5: Exploded view of the thermostat assembly-V10 engine

  1. Check to make sure that the thermostat valve closes tightly. If the valve does not close completely due to foreign material, carefully clean the sealing edge of the valve while being careful not to damage the sealing edge. If the valve does not close tightly after it has been cleaned, a new thermostat must be installed.
  2.  
  3. Immerse the thermostat in a container of warm water so that its pellet is completely covered and does not touch the bottom or sides of the container.
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  5. Heat the water and, while stirring the water continuously (to ensure uniform temperature), check the water temperature with a thermometer at the point when a 0.001 in. (0.025mm) feeler gauge can be inserted in the valve opening at a water temperature within plus or minus 5° of the standard thermostat temperature. If the thermostat does not open within the temperature range, replace it with a new thermostat.
  6.  
  7. Continue heating the water to a temperature of approximately 20° higher than the standard thermostat opening temperature. At this point, the thermostat should be fully open. If it is not, install a new thermostat.
  8.  

To install:
  1. To install, use a new gasket and position the thermostat so that its pellet end (the part with the spring) is toward the engine block. On the 3.9L engine, the vent hole must be up. Refit the thermostat housing and tighten its securing bolts to 25-30 ft. lbs. (34-41 Nm).
  2.  
  3. Connect the upper radiator hose.
  4.  
  5. On 1994-96 V6 and V8 models, install the alternator.
  6.  
  7. On V10 engines, install the two support rod mounting bolts and the support rod.
  8.  
  9. On 2.5L engines, remove the hex-head plug or vacuum switching valve on the thermostat housing. Fill the radiator with coolant until the coolant come out the plug hole. Install the plug or valve and continue to fill the radiator.
  10.  

Poor heater output and slow engine warm-up are often caused by a thermostat stuck in the open position: occasionally one sticks shut causing immediate overheating. Do not attempt to correct an overheating condition by permanently removing the thermostat. Thermostat flow restriction is designed into the system; without it, localized overheating due to turbulence may occur.

  1. On V6 and V8 engines, fill the cooling system to 1.25 in. (32mm) below the filler neck with the correct water and antifreeze mixture. Warm the engine and inspect the upper radiator hose and the thermostat housing for leaks.
  2.  

Diesel Engine

See Figures 6 and 7

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the coolant.
  4.  


CAUTION
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.

  1. Use a 3 / 8 in. drive breaker bar to lift the belt tensioner and remove the belt.
  2.  



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Fig. Fig. 6: Exploded view of the thermostat mounting-diesel engine

  1. Disconnect the upper radiator hose from the thermostat housing.
  2.  
  3. Loosen the alternator mounting bolts and lower the alternator.
  4.  
  5. Unbolt the thermostat housing and remove the housing engine lifting bracket and thermostat with seal.
  6.  

To install:
  1. Install the new thermostat to the housing, making sure the tang on the thermostat is aligned with the slot in the housing. This will ensure correct positioning of the jiggle pins in the housing. This is important because during filling, air vents through the jiggle pin openings through the upper hose and out the radiator fill neck.
  2.  



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Fig. Fig. 7: Be careful to install the diesel engine thermostat seal as shown

  1. Clean the pump mating surfaces.
  2.  
  3. Install the engine lifting bracket, new seal, thermostat and housing. Make sure the seal is installed with the beveled side facing out.
  4.  
  5. Tighten the thermostat housing bolts to 18 ft. lbs. (24 Nm). Connect the upper hose to the housing.
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  7. Reinstall the alternator into position. Tighten the upper bolt to 18 ft. lbs. (24 Nm) and the lower bolt to 32 ft. lbs. (43 Nm).
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  9. Install the drive belt.
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  11. Connect the negative battery cable, run the vehicle until the thermostat opens, fill the radiator completely and check for leaks.
  12.  
  13. Once the vehicle has cooled, recheck the coolant level. With the Thermostat plug on the relief valve removed from the thermostat housing, fill the radiator with coolant until the coolant comes out the plug hole. Install the plug or valve and continue to fill the radiator.
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