S350 Turbodiesel (W140) reliability

[Nautilus]

Hello everyone

My Dad has decided to part with our W124 for its larger sibling, the S 350 Turbodiesel (W140 series), as we found a Navy-blue model well in our affordability range.

As the S-Class complexity and parts costs are well-known, I wonder what are the most common mechanical problems of a 12-year old W140, and in particular the OM603 engine.

The car will be tested prior to acquisition, but no diagnose can tell the future.

Also I would like to know what are the maintenance requirements and especially those of the 4-speed automatic transmission, as this will be our first automatic on hand.

There is also the possibility of a chiptuning, as there are some workshops which offer customized chips for the ECU for more power (being a turbo, although not intercooled, some sizeable HP can be gained).

~Thanks everyone

Nautilus

[softconsult]

This engine has well known design flaws that cause the rods to bend and the cylinders to oval. Here is post from a well known expert on MB diesel engines in the US. This comes from www.mercedeslist.com. If your particular car already has the factory rebuilt engine, then you are fine. If not run away fast.

This makes some sense. Hydrolocking in some form may be an initiating
> cause. A little leak. A little bend. A little bend. An unbalanced
> load on the cylinder. Then the ovaling begins. Increased ovaling I've
> heard it blamed on dead glow plugs and / or head gasket leaks. While
> the fix your mechanic proposes may be possible, "He says the easy fix to
> prevent it all from happening is to remove the head, pull out the
> piston/rod assemblies (the engine can stay in the car)and replace the
> rods with the newer design now being offered by MB. Install a new head
> gasket and put 'er back together. Painless he says, and it can be done
> in a weekend." if the cylinders are not ovaled. If they are ovaled the
> block is toast (on a Friday no less). A compression test might help
> decide if the preemptive repair was worth trying.

There has been a lot of speculation about the rod bending properties of
the OM603.97 engine (Mercedes is silent on the subject), but despite
it's similarity to all the other Mercedes diesels produced during the
same period, the 603.97 was the ONLY one that developed the bent
rods/oval cylinders - and more than half of them have failed that way.
I have heard of two OM603.96 that have developed bent rods (but not the
ovaled cylinders) and maybe one or two 602.96 engines despite the fact
that MANY, MANY more of these engines were made. Then there is the fact
that once the rods were replaced and the cylinders were rebored and
sleeved, not a single OM603.97 engine has failed the same way. The
modified pistons (and several other modifications) used in early
rebuilds were determine to be of no benefit and were omitted from later
rebuilds.

A compression test is usually worthless until oil consumption is already
noticeably excessive (and by that time you already KNOW what's wrong).
The oil control rings fail to control oil consumption well before there
is any detectable compression loss. Bottom line is that the OM603.97
engine as released from the factory was flawed. The only reliable fix is
to replace the rods and rebore/sleeve the cylinders. Mercedes seems to
have a lock on the rebuilding process. I know of none of the Mercedes
rebuilds that have failed while more than half of the rebuilds done by
dealers, independent mechanics and rebuilders have subsequently failed.

Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" mbooth@pitt.edu
'87 300TD 182Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5 turbo 237kmi, '84
190D 2.2 229Kmi (retired)


Steve

[Nautilus]

Originally Posted by softconsult

If your particular car already has the factory rebuilt engine, then you are fine. If not run away fast.

Most likely it does not have it, and it has clocked 165,000km (about 102,500 miles)

We'll do the compression test and measure the consumed oil, though

I don't know (yet) the exact engine version (should check the papers in a few days)

~Nautilus

[t walgamuth]

i have a 90 350sdl so i have an interest in that motor.

only two slight disagreements with marshall.

first, i have heard of at least two here that have experienced bent rods on a factory replacement block.

personally i dont think the problem is weak rods. i think they are experiencing either hydrolock from leaking head gaskets or bending them on blobs of tar and or carbon. no rod in the world will sustain an attempted compression of fluid or solid material. they are designed to compress air only.

personally, if i experience a bent rod with mine i will rebuild with a 3.0 liter version of the 603 as these are not known to bend rods.

tom w

[Nautilus]

Thanks t walgamuth & softconsult

As an experienced owner, how would you rate the engine's way of driving (yours must be on a W126 bodywork, as the W140 production began in 1991, so it's a lighter car) ? Does it get good mileage (the factory numbers are unconvincing, it would be impossible for a gigantic car to burn as little as they claim)

Please let's gather together the pros and cons of the 350 TD W140 to make an informed decision

~Nautilus

[Hatterasguy]

You live in Europe hmm, why mess with the early diesel W140's? Buy a later one with a turbo charged 606. That engine is light years ahead of the 3.5L 603.

[rdanz]

Originally Posted by t walgamuth

i have a 90 350sdl so i have an interest in that motor.

only two slight disagreements with marshall.

first, i have heard of at least two here that have experienced bent rods on a factory replacement block.

personally i dont think the problem is weak rods. i think they are experiencing either hydrolock from leaking head gaskets or bending them on blobs of tar and or carbon. no rod in the world will sustain an attempted compression of fluid or solid material. they are designed to compress air only.

personally, if i experience a bent rod with mine i will rebuild with a 3.0 liter version of the 603 as these are not known to bend rods.

tom w

Can you give me the names of the two people with bent rods with factory replacement blocks?









































/

[DslBnz]

Originally Posted by Hatterasguy

You live in Europe hmm, why mess with the early diesel W140's? Buy a later one with a turbo charged 606. That engine is light years ahead of the 3.5L 603.

Too bad there were never available in the States.
If I liked the W140's type of style and routine upkeep, I may've considered one.

0-60 mph still takes 10 - 11 seconds, though. Not much quicker than the 3.5: When you're pulling all of that weight, performance suffers.

And it always puzzled me how the W140 S350 turbodiesel was claimed about as quick as the W126 with the same engine. Despite there being approximately a quarter-ton difference in weight.