I just heard an interesting comment about the quality of diesel engines.

The newer 126 8-cylinder engines have many more troubles than the older 5-cylinder engines.

What's your take on this?

The 3.5L diesel was a 6 cyl which has come to be known as the "rod bender". Said to have been the worst engine MB has made.

It was used in later W126 SDL's and all W140 300SD's and S350's from 90(?) up through 95. Some of the later long block crate replacement motors were said to have used updated rods. Some of them apparently failed too

The 5 & 6 cyl 3.0L diesels (eg: 617's, 602's & 603's) have all proven very reliable as has the 606 family.

Thank you, TMAllision.

I'm currently considering either buying a 2000 C230 or an older Turbodiesel.

Considering the economy, the turbodiesel would probably the saver bet.

Your valuable info is very much appreciated.

The updated motors used a new block that allowed the cylinders to stay round. That's what bent the rods....


Best 6 banger combo is the 3.5L with the replacement block. Second best is the 3L 6 in any form.


And to answer your question, the 6 bangers' are worlds better than the 5 cylinder timing chain eaters.

You'll get better mpg out of a modernish 6-cyl MB gas engine than you will an older TD.

I found that out.

I must really say I'm very much in favor of buying a 2000 or so E-class.

As much as I like my old 300D, I'm in the mood for some smooth power and speed.

Driving an S-class TD vs the old 300D's is like driving a Volvo and calling it a MB... No comparison. I was looking for a 300D untill I drove an SDL. Then I had to have one.

Like the SDL, tuna boats also wallow when manuevering aggressively and are underpowered for thier size.

Newer vs older tech (if one can afford it) is usually a no brainer.

Plenty of power on the SDL, you must be thinking of the 300D's...

I think you mean 6-cylinder, and yes, its true.

Early 3.0L engines were prone to cracking the head if allowed to get too hot.
All 3.5L engines are at risk for bending rods. It was a poor engine design and MB never officially acknowledged there was even a problem.

The 3.0L is a great engine if combined with a later head casting (#17-22), ironically, from the 3.5L.

I have one of the good ones. My 1991 350SD has 242600 miles on it and will still haul #$@! I've owned it for about eight years and it has been and still is one awesome car.
The engine failures that you speak of usually occur fairly early in life IF they are going to occur. Statiscally, less than 50% of the engines ever fail. Granted that is a high probability of failure. "All" is not a fair word.

The problem should be contributed to a factor other than a faulty design by MB if ALL engines are not affected.

Any thoughts on this?

could have been a metalurgy problem also.When I was a Machinist,some of our bearing races grew .030.

300sdl is no doubt powerful, quiet and smooth.

I've heard the same "bad" issues with the 350SD. HOWEVER, I had a 1991 350SD for over a decade and sold it a couple of years ago with 275000 miles on her. She would fly and I never had any motor issues with her at all. Great Car! Some of them did have issues...I had a good one!

My 350 has 116K and runs fantastic. You are also hearing that from a man that has owned many 617 diesels................You just can't rag them out, with very little service.

As much as a like a nice W126 and love a diesel, get those freaking AMG badges off of there. Since I live in virginia, I'll be sure to point and laugh if I ever see you drive by with that crap on your car. That includes the fender vents.. jesus christ almighty.

Apparently I have one of the good ones too (knock on wood). Almost 200k and no issues at all. It still hauls #$@ too, for a diesel. It's quiet and the ride is great. But any W126 "L" rides great.

The C230 will yield better fuel economy

Found a beautiful, 1991 350SDL, 113K miles, one owner, all service records. Price is a bit high, but this car (photos, at least) appears to be immaculate. If the engine, undercarriage, etc. are in similar shape, I might be inclined to buy it. This whole 'rod bending' issue has me worried, though. How can you tell if that's an issue before it's too late? Is there a way to know without tearing down the engine? I will definitely get it in to a mechanic before purchasing it - but an older man and his wife owned it and I think it's been well-cared for. But I also don't want to drop this kind of cash into a car that old, and then find out I need to put a new/rebuilt engine in it. Any advice?

Can anyone tell me if the 350SDL was a 49 or a 50 state car? I can't tell where to post a new subject for the W126 ...