Replacing and checking the thermostat (Audi 100 C3)

If the engine overheats but the radiator remains cold, this indicates a faulty thermostat. If a faulty thermostat is constantly open, the engine will not warm up to operating temperature. In these cases, the thermostat is replaced.

Execution order

1. Drain the coolant (see paragraphs 1–3 of subsection 4.1).

2. Loosen the bolts and remove the cover (5) (see Fig. Cooling system of a four-cylinder engine) or (16) (see fig. Cooling system of a five-cylinder engine) thermostat.

3. Remove the sealing ring from the lid.

4. Remove the thermostat from its socket.



5. Measure the distance a. Then heat the thermostat in water. The thermostat starts to open at about 87°C, and ends at about 102°C. After heating, measure the distance A. For a functioning thermostat, the difference between the distances A and a should be at least 8 mm.

6. Replace the thermostat cover sealing ring (see Fig. Cooling system of a four-cylinder engine, rice. Cooling system of a five-cylinder engine).

7. Install the thermostat into the socket so that the arrow on the thermostat crossbar points downwards.

8. Install the cover, tighten the bolts evenly and tighten to a torque of 10 N·m (1.0 kgf·m).

9. Fill the cooling system with liquid.

[The original version of the article is posted on the website AudiManual.ru]