GL Class (X164) 2007-2012: GL320CDI, GL420CDI, GL450, GL550

Loud Knocking from left side of engine when warms up.

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Old 03-28-2015, 10:28 AM
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Gl450
Loud Knocking from left side of engine when warms up.

Yesterday, my GL450 started a loud knocking. At first, I thought, OH NO! its a rod! But I don't think so. When the car is cold, the sound is not there. after about 20 or 30 seconds it comes in sporadic and then when the motor warms about 1 or 2 mins, it increases, it also increase in frequency with RPM increase but doesn't seem to be tied directly. Engine performance is fine. Runs fine, just this loud, embarrassing knocking. I notice it more on the left. Could it be tensioner or water pump? Oil? Maybe CAM? Not sure. The sound is almost like "Morse Code", but increases in TAPS as engine warms. Any ideas?



Last edited by Blmbryan; 03-28-2015 at 11:22 AM. Reason: Add link to video.
Old 03-28-2015, 09:57 PM
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alx
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Originally Posted by Blmbryan
Yesterday, my GL450 started a loud knocking. At first, I thought, OH NO! its a rod! But I don't think so. When the car is cold, the sound is not there. after about 20 or 30 seconds it comes in sporadic and then when the motor warms about 1 or 2 mins, it increases, it also increase in frequency with RPM increase but doesn't seem to be tied directly. Engine performance is fine. Runs fine, just this loud, embarrassing knocking. I notice it more on the left. Could it be tensioner or water pump? Oil? Maybe CAM? Not sure. The sound is almost like "Morse Code", but increases in TAPS as engine warms. Any ideas?


I would say it is a bad pulley bearing. Ideally you need a mechanics stethoscope to pinpoint the exact source
Old 03-29-2015, 08:04 AM
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Thank you for replyingl

Originally Posted by alx
I would say it is a bad pulley bearing. Ideally you need a mechanics stethoscope to pinpoint the exact source




I agree. Picking one up today. Using the "Screwdriver to the ear" method, it sounds like timing chain box, but hard to tell exactly. I was thinking timing chain tensioner. Maybe?
Old 09-12-2017, 06:50 PM
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2010 W212 E550 4matic
Did you figure it out in the end?

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