In this case, the thermostat continuously expands from size "a" to size "b".
Before removing and checking the thermostat, make sure that the engine cooling problems are not due to insufficient coolant or poor drive belt tension. Check the serviceability of the indicator located on the dashboard.
2. If you notice that the engine takes a long time to warm up to operating temperature (according to the indicator readings), the thermostat may be stuck open. In this case, the thermostat should be replaced.
3. On the other hand, a long warm-up may be due to the absence of a thermostat. This could have been done intentionally or unintentionally (forgot to install after repair). Do not operate the vehicle without a thermostat. The engine management system will keep the engine in warm-up mode for a longer period of time. During this time, the engine will consume more fuel and the exhaust gases will contain more harmful impurities.
4. If the engine is overheating, feel the upper radiator hose. If it is not hot and the engine is overheating, the thermostat may be stuck in the closed position. The fluid does not enter the radiator and circulates in a small circle. In this case, replace the thermostat.
5. If the upper radiator hose is hot, this means that the thermostat is open and the fluid is circulating normally in the system. In this case, read the recommendations given in the section Troubleshooting.
Examination
1. Remove the thermostat housing.
2. Check the position of the thermostat through the connecting pipe in the housing. Measure the dimension "a" on the thermostat.
3. If the thermostat is open at room temperature, it is faulty and must be replaced.
4. To roughly check the thermostat's functionality, hang its body on a piece of twine in a vessel with water. The thermostat body should not touch the walls of the vessel. Start heating the vessel.
5. As the water heats up, the thermostat should open (this happens just before the water boils). Since the boiling point of water is 100°C, the thermostat may not open fully (refer to Specifications). Remove the thermostat and let it cool. As it cools, it should close completely.
6. If the thermostat does not open when heating or does not close when cooling, replace it.
7. When installing the thermostat, keep the following in mind.
- 1. Thoroughly clean the mating surfaces and replace the sealing ring.
- 2. Place the thermostat into the housing, oriented correctly.
- 3. Tighten the cover mounting bolts to the required force.
- 4. Reinstall all hoses in their original locations, then fill with coolant (refer to Chapter Routine care and maintenance).
- 5. Start the engine, warm it up to operating temperature and check for leaks.
(The original text is available on the website: «AudiManual»)