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=pAvM_mz5y-GMVKXm
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=pAvM_mz5y-GMVKXm
Last edited by Potrice; Aug 27, 2025 at 08:24 PM.
Junior Member
Joined: Dec 2022
Posts: 56
Likes: 13
2012 MB R350 Bluetec
This is likely your vacuum pump, located at the top right of your engine. Easy to remove and replace.
But I am editing post to say that just make sure it's not one of copper seals on your fuel injectors (you should see small whiffs of smoke if these are leaking or you might see 'black death' around the leaky fuel injector, another sign is a fuel smell might enter the cabin through the air vents when the car is running)
I had to remove vacuum pump on my r350 bluetec, that was due to a minor oil leak at the vacuum pump, so all I did was replace the gaskets. Be careful not to over tighten the bolts. The people who worked on my car prior to my ownership had stripped the bolt holes on my vacuum pump bolts, which is why it was leaking oil. I had to install helicoils to properly tighten the vacuum pump bolts.
QUOTE=Potrice;9206406]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.
[/QUOTE]
But I am editing post to say that just make sure it's not one of copper seals on your fuel injectors (you should see small whiffs of smoke if these are leaking or you might see 'black death' around the leaky fuel injector, another sign is a fuel smell might enter the cabin through the air vents when the car is running)
I had to remove vacuum pump on my r350 bluetec, that was due to a minor oil leak at the vacuum pump, so all I did was replace the gaskets. Be careful not to over tighten the bolts. The people who worked on my car prior to my ownership had stripped the bolt holes on my vacuum pump bolts, which is why it was leaking oil. I had to install helicoils to properly tighten the vacuum pump bolts.
QUOTE=Potrice;9206406]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.
Last edited by Chrome988; Sep 1, 2025 at 11:47 PM.
Thread Starter
Senior Member
Joined: Nov 2015
Posts: 272
Likes: 49
From: Ottawa, Ontario
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
This is likely your vacuum pump, located at the top right of your engine. Easy to remove and replace.
But I am editing post to say that just make sure it's not one of copper seals on your fuel injectors (you should see small whiffs of smoke if these are leaking or you might see 'black death' around the leaky fuel injector, another sign is a fuel smell might enter the cabin through the air vents when the car is running)
I had to remove vacuum pump on my r350 bluetec, that was due to a minor oil leak at the vacuum pump, so all I did was replace the gaskets. Be careful not to over tighten the bolts. The people who worked on my car prior to my ownership had stripped the bolt holes on my vacuum pump bolts, which is why it was leaking oil. I had to install helicoils to properly tighten the vacuum pump bolts.
QUOTE=Potrice;9206406]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...vM_mz5y-GMVKXm
But I am editing post to say that just make sure it's not one of copper seals on your fuel injectors (you should see small whiffs of smoke if these are leaking or you might see 'black death' around the leaky fuel injector, another sign is a fuel smell might enter the cabin through the air vents when the car is running)
I had to remove vacuum pump on my r350 bluetec, that was due to a minor oil leak at the vacuum pump, so all I did was replace the gaskets. Be careful not to over tighten the bolts. The people who worked on my car prior to my ownership had stripped the bolt holes on my vacuum pump bolts, which is why it was leaking oil. I had to install helicoils to properly tighten the vacuum pump bolts.
QUOTE=Potrice;9206406]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...vM_mz5y-GMVKXm
Thanks for the info! Should I stick with OEM for the vacuum pump? There is a 500$-600$ difference in price OEM vs aftermarket...
Thread Starter
Senior Member
Joined: Nov 2015
Posts: 272
Likes: 49
From: Ottawa, Ontario
2013 ML350 Bluetec, 1966 Ford Mustang Convertible (sold)
This is likely your vacuum pump, located at the top right of your engine. Easy to remove and replace.
But I am editing post to say that just make sure it's not one of copper seals on your fuel injectors (you should see small whiffs of smoke if these are leaking or you might see 'black death' around the leaky fuel injector, another sign is a fuel smell might enter the cabin through the air vents when the car is running)
I had to remove vacuum pump on my r350 bluetec, that was due to a minor oil leak at the vacuum pump, so all I did was replace the gaskets. Be careful not to over tighten the bolts. The people who worked on my car prior to my ownership had stripped the bolt holes on my vacuum pump bolts, which is why it was leaking oil. I had to install helicoils to properly tighten the vacuum pump bolts.
QUOTE=Potrice;9206406]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...vM_mz5y-GMVKXm
But I am editing post to say that just make sure it's not one of copper seals on your fuel injectors (you should see small whiffs of smoke if these are leaking or you might see 'black death' around the leaky fuel injector, another sign is a fuel smell might enter the cabin through the air vents when the car is running)
I had to remove vacuum pump on my r350 bluetec, that was due to a minor oil leak at the vacuum pump, so all I did was replace the gaskets. Be careful not to over tighten the bolts. The people who worked on my car prior to my ownership had stripped the bolt holes on my vacuum pump bolts, which is why it was leaking oil. I had to install helicoils to properly tighten the vacuum pump bolts.
QUOTE=Potrice;9206406]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...vM_mz5y-GMVKXm
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.
Thanks again!
