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1991 350SDL Engine Question

9K views 13 replies 9 participants last post by  Brian Carlton 
#1 ·
I'm new to the site and I am looking at a 1991 350SDL and would be grateful for any advice. I think I can get the car for $2,500 and was about to make the deal before I did a little research. for obvious reasons, (Engine Failure) I am not certain this is such a great deal. The car runs and drives beautiful. Minor issues though, drivers window, no AC and some dings and dents. Is there any way I can verify if the engine has been replaced? I called the local MB dealer and since they didn't service the car they said they couldn't help.

VIN WDBC35E3MA598242

Thanks, Bill
 
#2 · (Edited)
Do a Google search on "350SDL rod bender" and read through the articles.

I would consider it as if you were just buying a body and planning on putting in a used engine. From that viewpoint IMO the price is way too high even if everything was perfect.

Edit:

As has been mentioned on other list unless this car has been perfectly maintained you can figure a minimum of $3k in repairs without even searching very hard. This car has obviously been treated poorly. Figure the $3k baseline. Add $2k for paint and body. Budget $1k for A/C. Budget $2k for purchasing and installing a used 300 engine. You should have $6k + the purchase price just to make this car safe and dependable. Then a minimum of $2k more to make it look nice. Generally for the diesels to get the car in like new condition you are going to spend around $8k. You are at that right now if they guy gives you the car for free and you find minimal additional items to repair.

Keep looking. You can find a much better deal. If the car was in perfect condition and you had additional cash for an engine replacement I would go for it. Not this one.
 
#4 ·
I think $2,500 could be a good deal. How many miles are on the car? Purchased mine with 135,000 miles on it for only $4000 about 5 years ago. Never had a mechanical problem with it in the 50,000 miles I have put on it. Don't believe that every single 350 will blow at anytime or is a ticking time bomb like every body says. There is a 350SD around where I live with 334,000 miles on the original engine. You won't find many 350's for less than about 3500 dollars unless the mileage is high or there is something else wrong. Would love to see some pictures of the car if possible. Good luck!
 
#5 ·
350!





Nice to see someone finally talking good about this engine. We all know they had issues but not all of them. Those engine purr like kittens.
 
#6 ·
Call another dealership. If you give them the VIN they are able to pull the service history on the car for all services done at an MB dealer. One would assume that a replacement engine would be done at a dealer.
 
#7 ·
Here is the link to the car.
PALM MOTOR COMPANY: 1991 Mercedes-Ben S Class

I have been searching the internet that's why I got cold feet. I had a 300TD and other than slow acceleration and the fickle rear suspension, I loved the car. ( Sold it last year) I drove this 350SDL and was blown away by the POWER. It seems like it could be good deal till I did a little research. Thanks for the replies and I am going to try another MB dealer to see if they can tell me anything.

2006 Vibe
1992 Bonneville SSE
1969 C10

Bill
 
#9 ·
Dredging-up this thread I found rather than start a new one, I'm looking for facts about the 350SD motor. What was the big change between the early 6-cyl. diesels, (OM603.961), and the later 3.5 version, (OM603.97)?

I've of course read all of the "rod bender" comments and advice to avoid this model. I've also seen the comments suggesting that MB corrected whatever issue these motors had somewhere early in their production run(?) And replaced a lot of faulty engines under warranty(?)

Looking for specific, factual information. No offense, but simply repeating wives tales from the internet doesn't help my education here. If you have actual experience with one of these later 3.5 OM603 engines, good or bad, by all means share it. Also any factual info about the design flaw(s) that doomed these engines.

Thanks a lot!
 
#12 ·
Looking for specific, factual information. No offense, but simply repeating wives tales from the internet doesn't help my education here. If you have actual experience with one of these later 3.5 OM603 engines, good or bad, by all means share it. Also any factual info about the design flaw(s) that doomed these engines.

Thanks a lot!

The actual facts are as follows:

The 3.5L engine has a slightly larger bore and a slightly longer stroke when compared to its 3L predecessor. Stuffing six cylinders into the block of the 3L was quite the feat and there is precious little space between those cylinders. M/B then decided to push the envelope a bit more, remove the liners, and open the bores a bit. This leaves the cylinders practically touching each other.

The theory is that the connecting rods are not quite up to the task and a certain percentage suffer a fatigue failure. You might know that the prediction of fatigue failures is more of an art than a science and it's impossible to predict if any one specific connecting rod will suffer from a fatigue failure unless its fatigue live is unlimited. M/B attempted to correct the problem with the rods by redesigning them several times, however there is no firm conclusion whether this absolutely solved the problem. I know of one specific engine that failed even with the updated rods.

Another fact is that it's virtually impossible to tell if a 3.5L engine has recently suffered bending of a connecting rod, or will suffer the fate in the future. The engine runs perfectly fine and idles well. It only starts to consume additional oil after the piston begins to ovalize the cylinder and the rings cannot contain the oil. During the additional oil consumption phase, it still runs perfectly fine. Even when the oil consumption has climbed to one quart every 250 miles, the engine still runs very well. It is at this point that the owner usually capitulates to the cost of the oil and the smog factor.

It is estimated (and this is not a fact) that about 30% of all the 3.5L engines will suffer from a bent connecting rod. The remainder will live their lives performing flawlessly with fantastic torque. The only question is whether you feel lucky?
 
#13 ·
Thank you, Brian! That's exactly the type of info that I was looking for. It's not that I doubt that those engines had/have issues, it's just that a lot of people knocking them, (pun intended), seem to be simply repeating a mantra with no clue as to what is actually wrong with them. It's confusing for me because I see them with 300k+ miles for sale still running strong like other (well-maintained) MB diesels.

I guess that the indication is oil consumption but that is hard to ascertain in a PPI unless the seller is really feeling honest. (Or guilty). I suppose excessive blow-by would be an indicator, just as it would be for any engine with bad ring-sealing. (Gas or diesel).

As for feeling lucky, I've found these cars for prices that make that gamble OK, assuming that they check-out at the present time for blow-by, etc...

Thanks again and keep the real-world experience coming! :thumbsup:
 
#14 ·
I guess that the indication is oil consumption but that is hard to ascertain in a PPI unless the seller is really feeling honest. (Or guilty). I suppose excessive blow-by would be an indicator, just as it would be for any engine with bad ring-sealing. (Gas or diesel).

As for feeling lucky, I've found these cars for prices that make that gamble OK, assuming that they check-out at the present time for blow-by, etc...

Thanks again and keep the real-world experience coming! :thumbsup:
You can never trust anybody with regard to oil consumption...................

Personally, unless you have your heart set on a W140, I don't see a good reason to procure a W126 with this engine when you could just as well find a decent W126 with the 3L engine ('86-'87).

If you do go for the W126 with the 3.5, you always have the option of finding a decent 3.0 to install in it. In fact, you could also accomplish the same thing in the W140 if the worst comes to pass.
 
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