S212 engine query

DoctorMesmer

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I acquired a 2015 S212 E220 Bluetec (OM651) last summer – my first Merc, first diesel and first automatic car. It has 85K on the clock but a FMBSH (and was last serviced 2-3 months before I bought it).

The car runs well, but I couldn't help thinking that my engine didn't idle as smoothly or quietly as I'd expected. It's possible to feel a small amount of engine vibration through the seat at idle – and in three side-by-side comparisons with friends' diesel cars, the Merc engine wasn't as smooth as a VW CC, a Passat or a BMW 525.

I took it to my local indy who took a look under the bonnet and said it sounded and felt normal. I also took it to the dealer, whose mechanic said the same. However, when he removed the plastic engine cover, I noticed that the metal air filter cover wasn't actually screwed down – the screws were rattling in their holes. It was likely an oversight from when the air filter was changed at the service. He screwed it down and that seemed to help.

However, I reckon it still makes more noise and vibration than I would have expected at idle. I don't think it's the engine mounts, and whilst the whole engine vibrates, it seems to be greater on the driver's side of the engine (around where the air filter cover is!) than the passenger side i.e. on your left as you look into the engine bay from the front.

I concede that I'm new to Merc and diesel and in day-today use, the car seems perfect. I had expected a smoother engine from Mercedes, though – diesel or not.

So...does this sound normal (as two mechanics have said) and are Merc diesel engines just that bit rougher than VW or BMW – or do I have a possible fault. If so, what might it be?

Thanks in advance for any replies.
 

FiveAlive

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The OM651 is somewhat agricultural and reviews at the time tended to note that it is a bit less smooth than contemporary rivals. From what you say it sounds like yours is normal - but try to compare it to another OM651 if you need to set your mind to rest.
 

ChrisHGTV

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I acquired a 2015 S212 E220 Bluetec (OM651) last summer – my first Merc, first diesel and first automatic car. It has 85K on the clock but a FMBSH (and was last serviced 2-3 months before I bought it).

The car runs well, but I couldn't help thinking that my engine didn't idle as smoothly or quietly as I'd expected. It's possible to feel a small amount of engine vibration through the seat at idle – and in three side-by-side comparisons with friends' diesel cars, the Merc engine wasn't as smooth as a VW CC, a Passat or a BMW 525.

I took it to my local indy who took a look under the bonnet and said it sounded and felt normal. I also took it to the dealer, whose mechanic said the same. However, when he removed the plastic engine cover, I noticed that the metal air filter cover wasn't actually screwed down – the screws were rattling in their holes. It was likely an oversight from when the air filter was changed at the service. He screwed it down and that seemed to help.

However, I reckon it still makes more noise and vibration than I would have expected at idle. I don't think it's the engine mounts, and whilst the whole engine vibrates, it seems to be greater on the driver's side of the engine (around where the air filter cover is!) than the passenger side i.e. on your left as you look into the engine bay from the front.

I concede that I'm new to Merc and diesel and in day-today use, the car seems perfect. I had expected a smoother engine from Mercedes, though – diesel or not.

So...does this sound normal (as two mechanics have said) and are Merc diesel engines just that bit rougher than VW or BMW – or do I have a possible fault. If so, what might it be?

Thanks in advance for any replies.
It sounds to me like the engine (and likely transmission) mounts are due for replacement. Do you feel any vibration on the side of the transmission tunnel inside the car? You shouldn't feel any. At 85k they are likely gone if not replaced already.

I only realised mine were shot when i had a W212 as a courtesy car - and that had just had new mounts. I got mine replaced immediately and it was a revelation - smooth, quiet and the gear changes also seemed much smoother. Best few hundred pounds ive ever spent on it.
 

grober

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The OM651 has twin Lanchester balance shafts driven of the crankshaft so should be quite smooth running. Although it hasn't done many miles if it has stop start the engine and gearbox mounts will have taken something like five times the impact strain from starting torque than an engine without-- renewing them would be a good first step.
12-arbres-equilibrage-lanchester-651.jpg
 
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DoctorMesmer

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Thanks for the replies so far.
I'll have the mounts checked when it's in for a service in a couple of months but I don't recall getting vibration through the transmission tunnel (and I tend to rest my leg against it so I'm sure I'd have noticed).
Yes it has start/stop (that only just started working again after it replaced the battery a couple of weeks ago). Maybe I'm wrong but balance shafts sound like an expensive replacement and not a DIY job!
 

grober

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Thanks for the replies so far.
I'll have the mounts checked when it's in for a service in a couple of months but I don't recall getting vibration through the transmission tunnel (and I tend to rest my leg against it so I'm sure I'd have noticed).
Yes it has start/stop (that only just started working again after it replaced the battery a couple of weeks ago). Maybe I'm wrong but balance shafts sound like an expensive replacement and not a DIY job!
Sorry I may have given the wrong impression by mentioning the Lanchester shafts it's just Mercedes used them as a form of centrifugal dampers to smooth out the engine. As such they would be subject to very little wear-probably the least likely of any of the moving parts to wear out!
quote:-
The operating principle of a balance shaft system is that two shafts carrying identical eccentric weights rotate in opposite directions at twice the engine speed. The phasing of the shafts is such that the centrifugal forces produced by the weights cancel the vertical second-order forces (at twice the engine RPM) produced by the engine.[3] The horizontal forces produced by the balance shafts are equal and opposite, and so cancel each other.
 

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