- The extraneous noise caused by a faulty hydraulic tappet occurs immediately after the engine is started and varies according to the engine speed. However, this noise does not depend on the actual engine load. Therefore, if the noise does not occur immediately after the engine is started, if it does not vary according to the engine speed, or if it varies according to the engine load, then the hydraulic tappets are not the cause of the noise.
- When a hydraulic tappet malfunction occurs, the noise almost never disappears even when the engine is idling after warming up. The only time the noise may disappear is when the engine oil is changed (the knocking of the hydraulic tappets in this case is caused by sedimentation in the engine oil).
Start the engine.
Make sure that the noise appears immediately after the engine starts and that the noise changes in accordance with changes in engine speed.
If the noise does not appear immediately after starting the engine, or if it does not change in accordance with changes in engine speed, the malfunction is not caused by a malfunction of the hydraulic tappets, look for another cause of the malfunction.
With the engine idling, check that the noise level does not change when the engine load changes (for example, when shifting the selector from position "N" to position "D").
If the noise level changes, the cause may be collision of parts due to wear of the crankshaft bearings or connecting rod bearing shells.
After warming up the engine, let it idle and check for any extraneous noise. If the noise has decreased or disappeared, the knocking of the hydraulic tappets may be caused by contaminated engine oil. Flush the hydraulic tappets.
Remove air from the tappets.
If the noise does not disappear even after bleeding the air, clean the hydraulic lifters.