Confirm my diagnosis: Engine mount failure
 

This morning (35*f) I noticed a louder version of a noise I had been hearing off and on for the last several days. Basically sounds like the engine is louder (this is the 98 E300 turbodiesel). The sound gets louder and quieter as I go over dips or high spots in the road. Louder on the downward dips, quieter on the upward ones. Also louder at higher RPM's. What is also puzzling me is it went away or at least got quieter as the car warmed. Would a bad mount be temperature dependent? I have not been under the car to measure, or is my mount theory way off base? No problems with the way the car starts, idles or runs. Thanks in advance for the help.

its really quite difficult to pinpoint what that could be, it could just be the cold, or it could be a subtle (in your case, noticeable) exhaust leak. if it were engine mounts, the everything would shake like a ***** and you'd know it. does it shake real bad? and i'm not talking on a cold start because i'm sure every one of our diesels on here will do some jarring and jittering on a cold start

good luck

How much vibration can you feel, at idle, through the steering wheel?

It should be practically non-existent.

Its an easy job to do:

http://forums.mercedesclub.org.uk/showthread.php?t=25921

Just make sure you pay attention to which side each mount goes on - they're not identical (a mistake I made!)

Doesn't shake but I have noticed an increased vibration through the steering wheel, very subtle but noticeable whereas before I didn't notice any. Unfortunately I have not records for the car so I don't know if they have ever been replaced.

Parrot:
Great DIY, I had to join the forum as I wasn't a member, but thats OK! Sorry you got them on the wrong sides, bummer. You mentioned the shake at shutdown, I have noticed that has increased also.

That sounds like a bad mount from your description and yes, temp does affect them as cold rubber is not a flexible as warmer rubber.

Usually the left (driver) goes first. Best to do them in pairs.

I would highly suspect the mounts and theres a way to check. If you have someone with a similar car with good engine mounts raise the hood, grab the intake manifold or whatever you can grab onto and try shaking the engine side to side or up and down (don't hurt your back trying). It should hardly budge in any direction.
Then do the same on your engine. A mechanic would use a floor jack under the engine to do the same test.
Greasybenz was just by the other day, complaining his fan was hitting the shroud. Well, I could put one and a half fingers between the fan blades and the shroud, his suspicion was the shroud was too low or too high or something.
So I did the "engine shake" test first on my '87 300D with new engine mounts then his. You could see that his engine was moving considerably, it was obvious the mounts were the problem and looking at L mount you could see it was coming apart.
I suspect bad mounts also put a lot of stress on the front flex disk so better check that also.

Thanks. Bear in mind that I live in the UK, and thus drive on the correct side of the road :P

Why is it that only MB's have engine mounts that need replacing?

I've never seen or heard of any other make that requires this repair.

Must be an age thing.....as a kid I had a 68 Camaro SS with a big cam that would take motor mounts out at idle.:D