rattling of the hydraulic tappets
When the engine is first started after a period of inactivity, a pronounced noise (frequent "clicking / rattling") of the working hydraulic tappets can be heard for a while. With a perfectly working engine, the noise disappears after warming up, damaged hydraulic lifters continue to rattle. This can be caused by contamination of the starting nozzles and/or wear on the hydraulic lifters. It is therefore first necessary to rinse these assemblies thoroughly. This can help to determine the cause of the rattling noises: If it is dirt, the knocking noises disappear after the starting nozzles have been flushed. If the hydraulic tappets are worn, the noise can be eliminated by increasing the viscosity of the oil or by changing the oil. A thicker oil seals the air gaps. If the wear on the hydraulic tappets is critical, they must be replaced.
Flushing the hydraulic valve lifter starting jets: VitaFlush - universal oil system cleaner to be added to the engine oil (from 200 to 1,000 km mileage).
Increase in oil viscosity: Atomex Complex Oil Treatment - Anti-Rauch Additive with Revitalizant®.
Adding the high temperature viscosity increased oil. For example, changing from oil with viscosity SAE 5W-40 to SAE 5W-50.
Experience shows that the use of Atomic Metal Conditioner TURBO, which has mild flushing properties, reduces tappet knocking.