Knocking sound
Thread Starter
Senior Member
Joined: Nov 2015
Posts: 272
Likes: 49
From: Ottawa, Ontario
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
Knocking sound
2013 ML350 BlueTEC with 357 000 km. Weird knocking sound coming from what seems to be the oil cap. The noise is present when I start the vehicle and let it idle but is dead silent once I arrive at my destination. Any idea? I initially thought the timing chain (still original) but the noise would always be present or only during a couple of seconds at startup when the engine is cold. This isn't the case. The suv runs fine, doesn't burn any oil and I change the oil every 10k km.
https://youtube.com/shorts/72-B5gVmuYc?si=M8EWfWzZyjZD_qlT
https://youtube.com/shorts/72-B5gVmuYc?si=M8EWfWzZyjZD_qlT
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
FANCY ROD KNOCK
2013 ML350 BlueTEC with 357 000 km. Weird knocking sound coming from what seems to be the oil cap. The noise is present when I start the vehicle and let it idle but is dead silent once I arrive at my destination. Any idea? I initially thought the timing chain (still original) but the noise would always be present or only during a couple of seconds at startup when the engine is cold. This isn't the case. The suv runs fine, doesn't burn any oil and I change the oil every 10k km.
https://youtube.com/shorts/72-B5gVmu...EWfWzZyjZD_qlT
https://youtube.com/shorts/72-B5gVmu...EWfWzZyjZD_qlT
This type of tricky rod-bearing knock has been heard before... only at cold idle and not warm idle.
I hear the knocking towards rear cylinders.
- Is this low oil pressure from oil pickup o-rings ?
- No coolant oil mixing anywhere ?
- No pressure loss at oil filter seals ?
- Any bearings shaving in oil filter ?
- What type of engine oil are you using ?
How about upgrading oil to hear how knock responds.
At any rate... don't "Italian-tune" /race this engine.
Last edited by CaliBenzDriver; Aug 28, 2025 at 01:18 PM.
Thread Starter
Senior Member
Joined: Nov 2015
Posts: 272
Likes: 49
From: Ottawa, Ontario
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
Problem solved
Problem solved. It was the vacuum pump that was starting to fail. I changed the vacuum pump (straight forward 30 minutes job) and the noise is completely gone. Hope this helps someone else.
