How do I Change the Thermostat on a Passat 1.8L?

Written by zyon silket
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How do I Change the Thermostat on a Passat 1.8L?
Working on the Passat is not much different than working on most American engines. (garage image by Gerd Reiber from

The thermostat in the Volkswagen Passat 1.8L is a mechanical thermostat, equipped with a spring-loaded jiggle valve designed to open as the temperature of the radiator fluid rises. The thermostat increases the flow of fluid through the engine, which in turn cools the engine temperature down. If the thermostat fails, it does so in the open position, which allows unrestricted flow of fluid through the engine. When this happens, the engine does not produce enough heat to warm the inside of the vehicle. During the summer, this is not an issue; however, in the winter, the lack of heat increases the need to replace the thermostat.

Skill level:

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Things you need

  • Pliers
  • Sealable container
  • Screwdriver
  • Adjustable wrench
  • 2 gallons of radiator fluid
  • 2 gallons of distilled water
  • Funnel

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  1. 1

    Drain the fluid from the radiator into a sealable container. To drain the fluid, open the petcock located on the lower-left side of the radiator with a pair of pliers. With the fluid drained, close the petcock and seal the container with the fluid to prevent children and animals from gaining access to the toxic material.

  2. 2

    Locate the water inlet tube. The easiest way to locate it is to trace the lower radiator hose to the location where the hose connects to the engine. On the Pasat, the water inlet is located directly below the water pump housing.

  3. 3

    Remove the hose from the water inlet tube. Loosen the band clamp that holds the hose on the tube, using a screwdriver, and then pull the hose off the tube.

  4. 4

    Remove the two bolts that secure the tube to the engine, using an adjustable wrench. Pull the inlet tube off the engine. Be cautious--the gasket and the thermostat tend to fall out with the inlet tube.

  5. 5

    Remove the gasket, O-ring (located inside of the inlet tube) and the thermostat, and then discard them. Inspect the inlet tube for any stress cracks of fractures. If you find any, discard the inlet tube and purchase a new one.

  6. 6

    Place the new O-ring into the water inlet tube. Place the new thermostat into the tube--the end of the thermostat with the spring sticks out of the tube. Place the gasket on the bottom of the inlet tube and place the tube back onto the engine. Secure everything into place with the two bolts.

  7. 7

    Slide the hose back onto the water inlet tube and secure it using the old band clamp.

  8. 8

    Drain a 50/50 mixture of radiator fluid and distilled water into the radiator via the radiator filler spout.

Tips and warnings

  • Do not change the thermostat while the engine is hot. It is likely that you will come in contact with the radiator fluid. If it is hot, you could be severely burnt. Wait until the engine is cool to perform this procedure.

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