What is this I keep hearing about the 3.5 liter turbodiesel six cylinder being troublesome? I believe "self-destructing" was a phrase I heard somewhere.

Can anyone explain what the problem is, and how many cars it affects. Also, which cars have the troubled engine?

What are the differences between this engine and the 3.0 liter six cylinder?

I ask because I have been trying to locate a newer car (bigger with better equipment) for my mom, something to replace the trusty '89 190D. This car has about 240k miles and is beginning to need more and more repairs. And it is also a bit underpowered when you get in some of the heavy traffic around here... It will go plenty fast (I've had it past 100) but it takes a long time to get there.

I have seen some mid-90s S350 turbodiesels for sale and was interested... until I heard about the 3.5 problems.


-Joe

XN6Guy,

I will try to contain myself and keep this short.

I had a 1991 350SD, bought it with 75,000 miles. It was a really impressive car, and if it had not suffered from the bending rod failure, I am sure I would have kept it for twenty or more years. Very good performer (a Diesel that could actually leave a patch from a stop sign), got very good mileage (about 27 mpg on the highway, about 25 around town), and was smooth, safe and spacious.

At 165,000 miles it suddenly began to use oil, developed a knocking noise at idle, and started smoking. I took it to the dealer figuring the valve seals had been worn out and ended up spending $7500 or so on a rebuild of the engine - new pistons, connecting rods, bearings, rings, and so on. The dealer told me they were unaware of what could have caused the problem, and told me it was certainly nothing I did.

At 175,000 miles it started smoking again. And I learned of this site. And I found out the engine suffered from a flawed connecting rod design/manufacturing issue. I asked the dealer how I could be assured the rebuilt engine was not failing due to the same problem and they either did not know, or elected not to tell me. So I complained as a 25 year customer to the salesman I work with, and he made me a fair offer in trade for the E300D TurboDiesel, which I took.

I have heard the theory that gunk in the inlet is suspected to be the culprit, when chunks get ingested into the engine. The gunk is a build up of exhaust gas recirculation line deposits, turbo oil seal leakage, and blowby routed from the valve cover. I think if that were the case, all Diesels would have bent rods because if you look at the inlets of any of them after 165,000 miles, they look pretty nasty. Also, the valves just don't open wide enough to allow a big enough chunk of that stuff to pass into the combustion chamber to have an effect like the engine ingested water or another incompressible fluid.

From the discussion of the number of design changes that have been implemented by Mercedes to address the problem, I have concluded the original rods (the same rods from the 3.0 liter engine however the 3.5 liter engine makes substantially more torque), if on the light side of the tolerance range, just did not satisfy a design norm for connecting rods in the automotive industry. They did not have an infinite fatigue life. As a result, some fail really early (in which case Mercedes replaced the engines or short blocks) and some fail later, and some (maybe most, but if yours fails that statistic is pretty meaningless) apparently never fail.

I now believe the revised rod designs, at least the last iteration, are probably ok. But putting a car in production that has a mechanical engineering design flaw like that is just not what is expected from Mercedes-Benz.

In the end, I really like the E300D TurboDiesel (it has traction control which tries to stop the wheels from spinning, but this car can make that orange triangle lite up with ease), and do not feel like I got abused financially, thanks to the salesman. While I would never buy a 350SD or any iteration using the 3.5 liter engine again, there probably are many good cars out there if you know what to look for, like quite a few miles, no knocking, no excessive oil consumption, and most importantly, good compression on all cylinders. I think I was lucky to have the dealership work with me, but if I had not purchased the car from the dealership I am sure I would have been on my own.

I don't want to condemn the car, as it is one of the best Diesel powered passenger vehicles you can drive, when it is running on all cylinders. And the one on EBay TXBill noted certainley seems to be healthy (plenty of miles, no unusual noises and no heavy oil usage were noted when the present owner went over it before he bought it and he was well aware of the issues with the car) but head in that direction only when you know the facts and be thorough in your examinations before you decide. I hope this helps, and good luck with your search. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

The 603 block motors have thier problems, mainly heads that crack, and with the 3.5 motor, the bent connecting rods. Like others have said, stay away from extrememely low mileage ones, like under 100K, or try to go even over 150K if you can find one, this only applies with the 3.5 motor, if you can find a low mileage 3.0, thats great.

If you really want a 6cyl diesel, you should look into an 86 or 87 300SDL, if you don't let them run hot then you don't have to worry about the head. My 87 300SDL has almost 270K on her now, original head, and i've owned it for the past 50,000 miles pretty much running at full-throttle all the time and have had aboslutely no engine or transmission problems.

I do have the 91 350SD up for sale on ebay, and at present time I honestly don't know of any engine problems with it, it really runs and sounds great and is also the fastest diesel I have ever driven, but will definately not leave a strip of rubber on the ground! I'm really not just saying this because I am selling one, but with 200K miles on the clock and purring like a kitten, I don't have any doubts about the engine's health.

To sum it up, if you do decide to buy a 3.5 diesel, look for a higher mileage one with no problems, for they have proven themselfs, the 3.0 sixes are great engines.

Joe,

Here's a link to some additional information and opinions on this engine:
To clarify, the OM603.96 engine was used in the '86-'87 S-Class SDL's and the OM603.97 engine was used in the S-Class diesels of the '90s to which TXBill referred. Good luck in your search.

__________________
Chris

'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold

Hmmm, interesting reading...

I think I'll stay away from that engine, just to be safe. What late model "S" class cars came with the 3.0 liter six? I assume an early 90s 300SD would have a 3.0 liter, but a good deal of literature indicates it has a 3.5 liter.

The 3.0 liter is safe, correct?

-Joe

Or one can just forget the 6 pot idea all together and go with a trusty 5! The 617 is a wonderful motor, which actually shares its lineage with a refrigerator motor from the 50's.... Anyway, while not nearly as fast as a 6, these motors pull well and are considered by and large one of the best (if not the best) motors Mercedes has ever made. Sure they are made of iron, and their valves need adjusting, you just can't kill a 617... A pioneer of Turbo power, these engines are a marvle... Just my two cents, of course, I am biased.

I totally agree about the 617, there is nothing like it, as Randall said, you just can't kill them, even with neglect.

My uncle and I raced his 86 300SDL (6cyl) and his 84 300D (5cyl) and it was very close, but the 300SDL eeked ahead at about 50mph and kept pulling.

The 617 is the old 3.0 liter 5 cylinder, correct?

I found some old "S" class cars (pre '86?) with this venerable 3.0 liter 5 cylinder, and it sparked my curiosity. However, I'd like to get something newer and more contemporary for my mom... that's why I initially considered an S350 turbodiesel. Plus, I fear that the big "S" style body combined with the 120bhp 5 cylinder wouldn't offer much of a performance improvement over her current '89 190D 2.5...

-BUT-

I think that I want to dip into Mercedes-Benz Diesel ownership, and I will definitely be looking for a 617 3.0 liter... There is just something magic about those early 80s Diesel Benzes, they have a certain luxurious but simplistic nature that I find incredibly appealing.

I absolutely LOVE diesel engines, and I'm the reason my mom even got that 190D in the first place. I currently own nothing but Peugeots, but I am looking to expand into other brands as well. I can give an endless list of reasons why I love Peugeots so much, and I think I could do the same for Mercedes-Benz too! I am an auto technician, with training and certification from Audi, Kia, and Chrysler... But I'd rather be under the hood of an old (but rust-free) Pug or Benz!

-Joe

An 81 to 85 300SD (3L 5cyl, 120HP) moves pretty good, its no sports car, but its no 240D. It can hold its own.

An 86 and 87 300SDL (3L 6cyl, 150HP) moves really good for a diesel, rivals a ford taurus or alike. Good engine and same MPG as the older 300SD, I get about 23 and I drive the car REALLY hard. Other members say they've gotten 30+MPG out of these land barges.

If I were you, I would just stay away from any 3.5 diesel, the 350SD, 350SDL, S350, S300.

Just to add my 2 cents....the 3.5 litre engine was troublesome in the US. MB claims that it is the quality of the US diesel fuel and that the euro versions didn't have any problems. I can't verify that, but I can tell you that the W140 body style was one of the most difficult and expensive cars to repair of all time. My dad's S500 was sold after it went out of warrenty and had its third $2500 repair within 5 months. The self closing door feature is usually the first to go followed closely by the automatic climate control. Thw W126 is much easier to work on...and less expensive too!

__________________
Old age and treachery will allways overcome youth and skill!

1993 S500
1984 380SL

Wow. A G350. I never imagined there was such a beast running around the streets of Europe.