Engine Knocking: Causes & Solutions

Hello everyone!!

"I've been experiencing the following problem with my Audi 100 AAT, 2.5 TDI for some time now..."

"When I start the car in cold weather, I sometimes hear a relatively loud clicking sound coming from the engine compartment. This sound then diminishes as the engine temperature increases, until it becomes almost inaudible."

At the same time, the engine is running slightly unevenly, and when it's warm, you can hear a kind of "muffled thumping" sound, which is quite faint if you put your ear near the oil filler cap.

The oil pressure seems to be okay, as the warning light goes out immediately when the starter is first turned. I would rule out bearing damage, as that usually gets louder with temperature... even under load, the engine is quiet, with no noises coming from the crankcase.

The car uses almost no engine oil.
It's definitely not a vacuum pump...

I've also opened the fuel injection lines while the engine is running, and the RPM drops equally for each cylinder.

My question is: could a faulty hydraulic lifter cause that?
If a hydraulic lifter is completely seized and can be compressed, wouldn't that cause the valve to have less lift, potentially leading to an uneven or erratic engine running?

Please provide advice, suggestions, etc.

Thank you!!!

Yes, that could be. However, the rumbling is independent of that and is generally normal.

Hello everyone...

Okay, now I know what's making that clicking sound.

The vibration damper has come loose, and in the process, it has damaged a corner of the crankshaft... what now?

"Thank you!"