1. This check should only be carried out on a cold engine, as the start temperature of the wax thermostat is +26°C.
2. On a cold engine, the valve must be positioned so that warm air can enter the engine.
3. Warm up the engine to operating temperature.
4. On a warm engine, the valve must be positioned so that only cold air enters the engine.
5. If not, then check if the valve moves easily.
6. If the valve does not work, it is necessary to replace the entire air filter housing.
Note. Recommendation: to test the wax thermostat, you need to warm up the sensor with warm air from a hair dryer - then the valve flap should move relatively quickly deeper. Drop some water and the valve should close quickly as well. If there is no movement, then the thermostat is faulty or blocked by a valve from below.