ML350CDI engine tapping noise

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benm

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Jun 4, 2010
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Hi, my W164 ml350cdi has started making a tapping noise from the engine. Sometimes it is barely audible and other times pretty loud. Possibly slightly worse hot than cold but hard to tell.
Had recent oil and filter change using approved MB229.52 oil. Car has done 150k miles. I suspected it may be the hydraulic tappets so tried some oil additive cleaner with no improvement.
Any ideas?
Is changing the hydraulic tappets an easy job on an OM642 engine?

Cheers

Ben.
 
Injector knock ?
 
I've had a knocking injector before on a different vehicle. Think this sounds different and no loss of power or rough running.
 
Would water in the diesel not eventually clear. Its been making this noise for the last 3000 miles now!
 
Not realy,, it will sit in the bottom of the tank and get mixed in for a few days after a fill up. Just had a boat tank emptied after being stood a couple of years, 40 ltr water and salvaged 180 ltr of fuel, all down to condensation. Any way of draining from the bottom..
 
Definitely worse on startup and low revs. When first started loud tapping for a few seconds then quietens down but still louder than normal.
Tried some injector cleaner but no better.
Still think it is the tappets but want to be sure before pulling the engine apart.
 
Definitely worse on startup and low revs. When first started loud tapping for a few seconds then quietens down but still louder than normal.
Tried some injector cleaner but no better.
Still think it is the tappets but want to be sure before pulling the engine apart.
How about taking off the engine cover and using a large screwdriver as a stethoscope to try and identify the source of the noise? This is just a suggestion that has worked for me in the past.

Ernie
 
How about taking off the engine cover and using a large screwdriver as a stethoscope to try and identify the source of the noise? This is just a suggestion that has worked for me in the past.

Ernie
That, and trying to gauge the frequency ie, crankshaft or camshaft speed. Also, it might be useful to check oil pressure (given the noise is worse at low rpm).
Anything that can 'drain' when sitting - eg. hyd tappets, timing chain tensioner, etc) - even though it shouldn't, can be noisy on cold start but should quieten quickly and remain quiet during running. You may have that and another source of knock present when running.
 
Did you do the oil change yourself, if you used a garage, they may have chucked in whatever oil they have at the time ( good reason to diy), I had a tapping vacuum pump on my old Focus ST, not sure if these engines use a similar item.
 
I'd be whipping the engine cover off and checking for leaking injectors first....varying volume with temp fits the bill...and they often sound more like tapping than the chuffing you would expect.
 
I'd be whipping the engine cover off and checking for leaking injectors first....varying volume with temp fits the bill...and they often sound more like tapping than the chuffing you would expect.
I did initially suspected the injectors but all are totally dry, no sign of leaks.
 
Did you do the oil change yourself, if you used a garage, they may have chucked in whatever oil they have at the time ( good reason to diy), I had a tapping vacuum pump on my old Focus ST, not sure if these engines use a similar item.
I did change the oil myself using the recommended MB oil. The tapping noise did start shortly after the oil change?
May have been a slightly heavier MB spec oil previously. I suspected some crud may have been dislodged and this would clear over time but not much change in noise several thousand miles later.
 

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