W126 560 SEL engine rumble under load
 

Ok.. been bugging me for a while. Been doing lots of work to make sure the engine is top notch. Vacuum leaks fixed, etc.

But when I put it under load, mainly (maybe only) at low speeds, the car will make a low end noise that I can only describe as a rumble. Its may also sound like a major missing or major engine retarding. Its a VERY noticable change in engine behavior. Sounds like it comes from the right side. When it happens the car also seems to dog down big time.

I can probably get a recording if needed.

The car has newer injectors, wires and dist. I am taking the dist apart later tonight to inspect. I just pulled the plugs, they were gapped at 0.045 and I reduced them to 0.032". But it was doing it before this.

Thoughts?

I don;t want to scare you (sometimes, people blurt out some "out-of'left-field" crap) but I had a car that did what you are describing and it was the timing belt. It was not a mercedes though so it could be something else. :)

How could it be the belt? Is it worn so bad it stretches really far under load? All my cars had timing chains, so this belt crap is new to me.

I suppose the only way to inspect is to remove the entire front end of the engine, cover, accessories, etc.

Take a look at both motor mounts, particularly on the side you think the sound is coming from. They definitely do not last forever.

These things use liquid mounts, right? A mount would make sense and the drop in power may just be.phycological

i vote for motor mounts.

The engine mounts on your car are not fluid filled like the newer cars,they are just rubber mounts which are prone to collapsing.

Robert

When the mounts go on a 560SEL, you will often hear the fan blades hit the shroud on hard acceleration from a stop. The sound that makes sounds a lot like a power steering pump with buggered internal parts; metallic and grindy. Just pop the hood up and do a brake stand, you'll know right away if the mounts are shot; the engine will jump around noticeably.

Be careful though. In my case, a piece of the fan blade broke off and stabbed through the radiator, ruining it.

Inspect your flex discs, make sure they aren't about to go as that can be quite nasty, and can even set off the airbag.

Flex discs look new. I took a very close look at em. A lot of work was done by the PO.

I dont hear the fan blades, but I will sure try to see what happens when I got at her with hood open.

I too vote for motor mounts, or trans mount.

Holly monkey balls! Engine almost lifted right out. I bet only the exhaust is keeping it down. Drivers side lifted right up and sure enough under less intense revs the fan would scrap. Checked for blade damage, none so far...

I will price out mounts and see what is into replacing them. I hope its not too big of a project.

Don't drive it until you get the mounts replaced, which is not a big deal or too expensive. You'll wind up like me with a new radiator and a thinner wallet.

After inspecting the damaged radiator, I realized that the blades were not hitting the shroud, they were hitting the very bottom of the radiator! Make sure to inspect the radiator near the bottom center to make sure it hasn't done anything more than mash a few fins. I would have been fine had the little piece of the fan blade not broken off.

Well I have to drive it. But I am taking it easy on the load and it is fine thus far.

Have two new mounts coming Monday. $26 for the pair. Love dealer pricing! :D

good to hear that it was a simple fix....:)