VW Passat & Audi A4 1990-2000

Thermostat

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REMOVAL & INSTALLATION

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.


NOTE
Apply an anti-seizing compound to the thermostat housing fastener threads before reinstalling them.

All 4 Cylinder Models

The thermostat is located in the bottom of the water pump housing.

  1. If equipped, remove the lower engine shield.
  2.  
  3. Place a large drain pan under the vehicle to collect the coolant.
  4.  
  5. Remove the radiator cap and drain the cooling system into a suitable container.
  6.  
  7. On 1.8L engines, remove the water pump housing drain plug.
  8.  
  9. Loosen one bolt at a time until coolant begins to flow.
  10.  
  11. Remove both bolts and remove the thermostat.
  12.  



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Fig. Remove the housing bolts



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Fig. Once the bolts have been removed, pull the thermostat housing away from the bottom of the water pump unit



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Fig. Note the position of the thermostat and gasket



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Fig. The 1.8L engines have a water pump drain plug near the thermostat housing



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Fig. An exploded view of the water pump, pump housing and thermostat-1.8L engine illustrated



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Fig. The 1.8L water pump, drain and thermostat housing

To install:

  1. Install the thermostat using new O-ring.
  2.  
  3. If removed, install the water pump drain plug with a new O-ring and tighten to 22 ft. lbs. (30 Nm).
  4.  
  5. Torque the housing the bolts to 88 inch lbs. (10 Nm).
  6.  
  7. Top off cooling system with the recommended fluid and concentration. For additional information, please refer to the following topic(s): General Information And Maintenance, Fluids And Lubricants.
  8.  

2.8L VR6 Engine


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Fig. Exploded view of a VR6 thermostat housing

The thermostat is mounted in the housing and located on the rear of the cylinder head.

  1. Drain the engine coolant into a suitable container.
  2.  
  3. Remove the mounting bolts from the flange.
  4.  
  5. Remove the flange and the thermostat.
  6.  

To install:

  1. Install the thermostat with a new O-ring.
  2.  
  3. Install the thermostat housing.
  4.  
  5. Install and tighten the fasteners.
  6.  
  7. Top off cooling system with the recommended fluid and concentration. For additional information, please refer to the following topic(s): General Information And Maintenance, Fluids And Lubricants.
  8.  

2.8L V6 Engines

The thermostat is located in the engine block just to the side of the water pump underneath the housing where the upper radiator hose is attached.

  1. Remove the lower engine shield.
  2.  
  3. Place a large drain pan under the vehicle to collect the coolant.
  4.  
  5. Remove the radiator cap and drain the cooling system into a suitable container.
  6.  
  7. Place a large drain pan under the engine block drain located at the bottom of the engine near the vicinity of the flywheel and the oil pan.
  8.  
  9. Drain the engine block coolant into a suitable container.
  10.  
  11. Place the (hood) lock carrier in the "service position". For additional information, please refer to the following topic(s): Body And Trim, Service Position, Front Bumper, Hood Lock Carrier.
  12.  
  13. Remove the accessory drive belt. For additional information, please refer to the following topic(s): General Information And Maintenance, Routing Maintenance And Tune-Up.
  14.  
  15. If installed, remove the upper front engine cover.
  16.  
  17. Remove the toothed camshaft drive belt from the right side cylinder head to allow enough access to remove the thermostat housing. Cover and protect the drive belt from residual coolant.
  18.  
  19. Remove the mounting fasteners; remove the housing, then the thermostat.
  20.  



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Fig. An exploded view of the water pump, thermostat housing and thermostat-2.8L V6 engines



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Fig. Lubricate the O-ring with coolant and make sure the thermostat is installed with the bleeder facing up-2.8L V6 engines

To install:


WARNING
The thermostat vent valve must be installed facing up otherwise the cooling system may develop air pockets and allow the engine to overheat.

  1. Using new O-ring, install the thermostat making sure the vent valve is installed facing up.
  2.  
  3. Install the thermostat housing and torque the housing the bolts to 88 inch lbs. (10 Nm).
  4.  
  5. Inspect the camshaft drive belt for wear and damage and replace if necessary. If contaminated with fluids or lubricants, it should be replaced. For additional information, please refer to the following topic(s): General Information And Maintenance, Routine Maintenance And Tune-Up, Engine And Engine Overhaul, Timing Belt And Sprockets.
  6.  
  7. Installation is in reverse order of removal noting the following:
  8.  
  9. Top off cooling system with the recommended fluid and concentration. For additional information, please refer to the following topic(s): General Information And Maintenance, Fluids And Lubricants.
  10.  

 
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