How to Replace the Thermostat in a 1998 VW Jetta

Written by jeffrey caldwell
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How to Replace the Thermostat in a 1998 VW Jetta
(Jupiterimages/Comstock/Getty Images)

The thermostat in a 1998 Volkswagen Jetta is a small, temperature-control valve located in the cooling system. It controls the flow of coolant between the engine and the radiator. It is not unusual for a thermostat to become stuck in the closed position, preventing coolant from flowing and cooling the engine. If the vehicle is driven in this circumstance, the engine will overheat and extensive damage could occur. Replacing the thermostat on a 1998 Volkswagen Jetta is a relatively simple task that can be accomplished by the vehicle owner in about 2 hours.

Skill level:
Easy

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Things you need

  • Wrench set
  • Automotive jack
  • Jack stands
  • Waste oil collection pan
  • Rag
  • Flat blade screwdriver
  • Socket set
  • Replacement thermostat
  • Replacement sealing ring
  • Antifreeze
  • Water

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Instructions

  1. 1

    Disconnect the negative cable from the negative battery post, by loosening the retaining bolt on the cable end with a wrench. Then pull the cable end off the post.

  2. 2

    Raise the front of the Jetta using an automotive jack, and support withe front of the Jetta with jack stands placed underneath the frame.

  3. 3

    Under the front of the Jetta, locate the lower radiator hose connection to the radiator on the bottom of the radiator. Place a waste oil collection pan underneath it.

  4. 4

    Place a rag over the expansion tank cap and rotate the cap counterclockwise slowly to relieve the pressure.

  5. 5

    Loosen the hose clamp that secures the lower radiator hose to the radiator, using a flat blade screwdriver.

  6. 6

    Slowly pull the lower radiator hose off the radiator and allow the coolant to drain into the waste oil collection pan.

  7. 7

    Slide the lower radiator hose back onto the radiator. Tighten the hose clamp that secures the lower radiator hose to the hose clamp, using a flat blade screwdriver.

  1. 1

    Loosen the bolts that secure the power steering belt to its mounting bracket, using a socket. Then slide the pump toward the engine, relieving pressure on the V-belt, slackening it.

  2. 2

    Lift the V-belt off the pulleys and remove it from the vehicle.

  3. 3

    Unscrew the bolts that connect the power steering pump bracket to the engine, using a socket.

  4. 4

    Lift the pump and bracket out of the way, but do not disconnect the hydraulic hoses.

  1. 1

    Locate the thermostat housing. It will be connected to the lower radiator hose at the base of the water pump housing on the front right-hand side of the engine.

  2. 2

    Loosen the hose clamp that connects the lower radiator hose to the thermostat housing, using a flat blade screwdriver.

  3. 3

    Pull the lower radiator hose off the thermostat housing, using your hand.

  4. 4

    Unscrew the two bolts that secure the thermostat housing to the water pump housing, using a socket.

  5. 5

    Pull the thermostat housing off the engine, using your hand. Do not pry between the thermostat housing and the water pump housing using a screwdriver. Doing so may cause future leaks.

  6. 6

    Pull the sealing ring from the thermostat housing and discard it.

  7. 7

    Pull the thermostat from the water pump housing.

  1. 1

    Slide the new thermostat into position in the water pump housing.

  2. 2

    Insert a new sealing ring into position in the thermostat.

  3. 3

    Lift the thermostat into position on the water pump housing.

  4. 4

    Screw in the two bolts that secure the thermostat housing to the water pump housing, using a socket.

  5. 5

    Slide the lower radiator hose onto the thermostat housing. Tighten the hose clamp that secures the lower radiator hose to the thermostat, using a flat blade screwdriver.

  1. 1

    Move the power steering pump and bracket back into position.

  2. 2

    Screw in the bolts that secure the power steering pump bracket to the engine, using a socket.

  3. 3

    Lay the V-belt over the power steering and crankshaft pulleys.

  4. 4

    Slide the power steering pump away from the engine and tighten the mounting bolts using a socket.

  1. 1

    Slowly fill the expansion tank to the MAX line with a 50/50 mix of antifreeze and water. Filling the tank slowly will prevent air from being trapped in the cooling system.

  2. 2

    Squeeze the upper and lower radiator hoses to push out any trapped air.

  3. 3

    Add coolant if necessary, to bring the level up to the MAX line on the expansion tank.

  4. 4

    Lower the expansion tank cap onto the tank. Press down on the cap and turn it clockwise.

  5. 5

    Lower the vehicle.

  6. 6

    Reconnect the ground cable to the negative battery terminal. Slide the clamp over the terminal, then tighten the retaining bolt using a wrench.

  7. 7

    Run the engine and visually inspect for leaks.

Tips and warnings

  • You can by coolant that is already a premixed 50/50 blend of antifreeze and water.
  • The scent of antifreeze is highly attractive to pets. It is also highly toxic. Keep small children and pets away from antifreeze.

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