Audi A4 thermostat check

1 . Preparing to test the thermostat. When the engine warms up, the thermostat turns on a large cooling circuit. At the same time, the thermostat expands continuously, from size “ a ” to size “ b ”. Before removing and checking the operation of the thermostat, make sure that engine cooling problems are not due to insufficient coolant or loose drive belt tension. Make sure the indicator on the dashboard is working.

2 . If you notice that the engine takes a long time to warm up to operating temperature (as indicated by the indicator), the thermostat may be stuck open. In this case, the thermostat must be replaced.

3 . On the other hand, a long warm-up may be due to the lack of a thermostat. This could have been done on purpose or unintentionally (forgot to install after the repair). Do not drive the car without a thermostat. The engine management system will keep the engine in warm-up mode for a longer time. During this time, the engine will consume more fuel, and the exhaust gases will contain more harmful impurities.

4 . If the engine overheats, feel the upper radiator hose. If it's not hot and the engine is overheated, the thermostat may be stuck in the closed position. The liquid 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, the thermostat is open and fluid is circulating normally through the system.

6 . Checking the thermostat. Remove the thermostat housing.

7 . Check the position of the thermostat through the connecting pipe in the housing. Measure the " a " dimension on the thermostat.

8 . If the thermostat is open at room temperature, it is defective and must be replaced.

9 . For a rough check of the thermostat's performance, hang its body on a piece of twine in a vessel of water. The thermostat housing must not touch the walls of the vessel. Start heating the vessel.

10 . 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. Remove the thermostat and let it cool down. As it cools, it should close completely.

11 . If the thermostat does not open when heated or does not close when cooled, replace it.

12 . Installing a thermostat. Thoroughly clean the mating surfaces and replace the O-ring.

13 . Place the thermostat into the housing, orienting correctly.

14 . Tighten the cover bolts to the required torque.

15 . Install all hoses in their original places, then fill in the coolant.

16 . Start the engine, warm up to operating temperature and check for leaks.

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Source:  http://carmanz.com/audi/a4-b6-2000-2004/6514-a420003-1-5.html