I'm new to this forum, and to AMG, after some time with BMW's, so my apologies for what might be a newb question, but couldn't find the answers I was looking for in a search.

Just had my c55 diagnosed with a leaking LHS Engine Mount, and a RHS mount that is "soft" by the dealer.
The car is under warranty for another 2 months or so, but the dealer only wants to replace the LHS mount as he says that the RHS one is still OK, and that it is normal for it to last longer than the LHS as one side typically takes most of the strain.

Every time I've seen this done, both engine mounts are usually replaced, so this doesn't make sense to me, and I think he's just trying to put if off until the car is out of warranty. I'm insisting that he replaces both, but want to present some good arguments why.

Are any of you aware if there is any evidence to suggest that one side will wear significantly faster than the other and if he is correct?

Better still, is anyone aware of any Mercedes Service bulletins that recommend replacing both at the same time that I can refer to?

P.S. the car is Australian delivered and RHD if that makes any difference.
Thanks in advance for your help.

Welcome to the forum!

As far as engine mount wear is concerned, I personally can think of only two reasons why the engine mounts would wear unevenly.

1. Heat
I own an old 1989 300E, RWD, inline six engine.
On this car, the passenger side engine mount is known to usually fail first since it is located directly beneath two very hot exhaust manifolds and with-in inches of the pipes that lead from the exhaust manifold and travel underneath the car.

On the V8 car such as the C55, you have a hot exhaust manifold running on either side of the engine block. So in any RWD V6/V8/V10/V12 powered car, I would think each engine mount would be equally effected by the heat related wear from the engine.

2. Wear (From Torque)
So this is pretty obvious, but when you rev in engine in park while looking at the engine itself, the assembly may lean to one side a bit before returning to its nominal resting position. One engine mount is under compression and the other is in tension (being stretched apart) during that brief instant.

Here is a good article on eHow:
http://www.ehow.com/way_5949884_do-m...problems_.html

Hope this helps, the C55 is my first V8 car, always owned I6s before.

Thanks Rahulio,
I've had plenty of V8's before, (BMW, Ford, and GM mostly) but i've always replaced engine mounts in pairs, as whenever one has broken, the other was usually not too far away. (Except in one notable occasion in a Mazda with a transverse V6.)

The dealer is blaming torque, exactly as you described in (2), and trying to convince me that RHS mounts don't fail as much as LHS, because the LHS is under more strain?

Unless the mounts are affected more by either tension, or compression?

My guess, and this is just a guess, is that tension would damage an engine mount more rather than compression.

An engine mount is typically made of metal, rubber and some kind of dampening fluid. It guess it would be easier to destroy an engine mount by trying to pull the parts away from each other rather than compressing them together.

It makes sense mechanically to me, but that is about it.

It is a common problem for these cars, the mounts are universal for all w203's from the 4 bangers to the v8. I broke both mine at 45K and the tranny mount is complete garbage as well. All the torque will compress the passenger mount which is usually first to break. The E55 have a torque strap to prevent that you can make one with chains, which is my next project along with filling the tranny mount solid with silicon.

Thanks Kent426,
That sounds exactly what the dealer suggested.
The passenger side, (LHS on Australian cars), is the one that has failed first.
Is the torque strap an easy replacement?
Filling them with Silicon sounds like an interesting fix that could make them last longer as well anyway?