The 603.970 is a USA (North America) only engine, used in the W126. However the 603.971 was used in both USA and Europe, in the W140. They are essentially identical long blocks, with different exhaust manifolds and injection pumps.

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Dave
Boise, ID
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All your examples above relate to either an inept mechanic doing something he ought not, or an inexperienced driver doing something abnormal (i.e., overrevving) which subsequently caused the damage.

On the 3.5L OM603 failures, neither scenario applies, not even remotely. These engines failed in huge quantities (statistically) under normal everyday operating conditions. Your scenarios cited above simply do not apply in this case, not in the slightest. Especially given the OM60x family's heritage of near zero bottom end failures under any circumstances, even when pushed to double or triple their original power output (the Finns routinely do this with 2.5L and 3.0L OM60x engines, with again, almost zero failures). Yet the 3.5L can't even cough up a lousy 148hp/230tq without bending rods? Hmmmmm.

Why can't you accept the probability that the original 3.5L rods were simply too weak? That's what MB came up with as a solution (new, stronger rods) and - gasp - it worked.

Wonderful -- so you know for certain that the rod design used in the 603.970 is identical to that used in the 603.971 ?

If we assume that the Mercedes factory documentation in the EPC is accurate, then yes. The connecting rod was updated four times on the 603.970, here are the four part numbers in order:

603-030-19-20 (original rod)
603-030-22-20
603-030-25-20
603-030-32-20
603-030-29-20 (current rod)

The 603.971 has the same supercession sequence except that it started with the #22. It appears the #19 rod was only used on early .970 engines and never the .971 engines. The .970 was used in 1990-91 model years only, the .971 was used from 1992-up.

The footnote on the supercession states "ONLY REPLACEABLE BY THE SET - THE OLD PART MUST NO LONGER BE INSTALLED IN THIS PLACE", meaning MB wants you to install six of the #29 rods any time an older rod fails.

Sorry, I simply disagree.

An inexperienced owner could easily try to start a recalcitrant engine in cold weather and damage it. Simply neglecting to have the proper grade oil could cause this.

I am sorry, I simply disagree. The difficulty is that one needs to identify the underlying causal relationship [shared] between one set of statistical anomalies and another. The earlier and smaller displacement 603.961 has a high rate of tensioner failure. You are also assuming that (say) an induced triple the output with controlled combustion is equivalent to the stress of the spikes found with chaotic combustion.

I just look at data differently, I suppose.

Now THAT I can agree with.

So, it is clear that the .971 engines DO NOT share the original rod design.

Aside: if you redesign a rod to a pattern with equivalent but redistributed mass it is highly likely that you have altered the dynamic balance qualities.

The first rod, no. But the next three in the sequence were equally bad. MB got it right on the fifth attempt after about 5 years. The .970 engines used bad rod design #'s 1, 2, 3, and 4 before getting the "good" one. The .971 engines used bad rod design #'s 2, 3, and 4 before getting the good one. The "original" design is somewhat irrelevant as the early .971 engines experienced the same failures, at least through mid 1995 model year production, which is roughly when the final rod iteration was released.

The original design is not irrelevant if you are attempting to do a statistical analysis of (purportedly) worldwide data. Correct? Yes, I do look at data a bit differently, don't I ?

Now, I welcome the presentation of worldwide data of .971 engines with the first redesign, i.e. their original equipment at least to a given time in production. My hypothesis predicts that there will be distribution of this particular failure that positively correlates with a given range of cold winter climates (amongst many other possible variables).

Prove the prediction of my hypothesis to be incorrect.

Thank you.

It's YOUR hypothesis. YOU prove it. I am not going to do your work for you, and neither will anyone else.

In the meantime, all you have is a hypothesis: not a proven root cause, nor a fix that is anything different than what has been working for the last 15 years - new rods.

This is a weak response.

So far, my hypothesis accounts for the observed data as well as data from the failure of other erstwhile unconsidered components. This puts it in advance of your hypothesis. Schade. Yes, we two do look at data a bit differently.

I am inviting my hypothesis to be disproven and even saying specifically how it can be disproven. You don't wish to pursue that ? Oh well.


Edit: forgot to say that I do present a "fix" -- sorry that it is not more obvious -- do not allow the engine to run chaotically. Oh -- the failures of the other components I identified do persist to this very day, do they not ? And irrespective of strengthened rods to boot. Sigh.

How do you propose using the wrong grade of oil would cause a cold engine to bend rods? Extra friction? I would be very surprised if the starter were strong enough to bend a connecting rod.

Most of these motors died an early death, under the care of the original owners. Because they were able to afford the car in the first place I would assume they had the funds to have it serviced. Following that train of thought the friction required to bend the rods with the starter would be so great the car would crank over very slowly, and probably not start at all! The owner would certainly take the car to a shop for the "bad cold starting" problem.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I very specifically asked the service manager if there was anything I did that could have caused the rods to bend in my 350SD, and was told "no." I get the idea from your post you think abuse is the issue, and while I wondered about that and asked, as noted, I think the manufacturer is obligated, if they have a reputation in the industry to uphold, to design the machine for normal, non-engineering experts to drive in situations encountered every day. Taking a wrench to the engine and being ignorant about what you are doing is certainly outside the realm of "normal" design requirements. I designed equipment for US Navy nuclear submarine propulsion plants for 25 years. In that job designing so someone under unimaginable pressure to make a repair correctly, in the dark, etc... requires that one also consider how things might be done incorrectly. I get it that the bar is somewhat lower for commercial hardware.

If this paragraph is intended to suggest the customer assumes the risk of the preeminent Diesel powered passenger car designer and manufacturer delivering product that fails randomly and in a big, costly, way for known if not quantified "chaotic" Diesel firing events, I don't agree. If producing a Diesel version of the automobile is now beyond the capability of the manufacturer - their prior products were perceived to be so much more reliable, MB charged a premium for the Diesel versions of the S Class, as they do today for the ML320 CDI - and they do it anyway, that is something that is revealed by acquiring operating time on the engines and is hardly a reasonable risk for the customer to assume. MB did not live up to the standard of Toyota and Lexus on this one. Customer relations dictated they should stand behind the product and they, as a company, did not. My dealership did, for me, in the end. But MB didn't.

If chaotic firing of the injected charge of Diesel fuel is the issue, and it may very well be, there is nothing "new" about the probability of the event, or the fuel that was not on the "table" when the engineers designed the engine. Previous models with less aggressively designed engines did not have the problem. Later models with more torque and power from a smaller displacement do not have the problem. Same fuel, same propensity for chaotic firing (unless that is also "in the design space"), no bent rods or perhaps more accurately stated, no engine failures that have been attributed to bent rods. Hell, they may all bend a bit and all those other engines just didn't care.

I agree the TC tensioner design may not be a flawed design - abuse causing a failure of a part is one thing but really depends on the definition of abuse. Your case with the tensioner is clearly abuse as you defined it - some may feel the lack of some warning not to turn this engine backwards, yet the rest of the manufacturer's designs can be turned backwards without abusing them is a sign that some internal design standard was ignored. If the consequences were innocuous, no one cares. If the engine falls apart as a result, the parsing of blame becomes more intense.

But in the case of MB's bent rods the cause, if it is chaotic ignition of the injected charge that is a known potential event, then chaotic ignition of the charge loading is something that has to put on the list of tasks the engineer designing the system has to address. If the design allows the chaotic event to occur then the customer is hardly abusing the machine by running it and cannot be held responsible. And it seems the later engines this particular issue has been addressed. The 1998 E300D TurboDiesel I own now has over 210,000 miles. It is more powerful than the 350SD, quieter, more fuel efficient and uses next to no oil, still. So, MB can get the job done, chaotic Diesel fuel ignition characteristics or not. On the 350SD they didn't and suggesting the customers are abusing the vehicles to cause rods to bend is contrary to customer experience with MB's prior and post 603.97X series of Diesel engines. It is also a "lower the engineering standard" stance that no one needs to help MB invoke.

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)

I would also argue agains the chaotic firing theory, my 350SDL starts and idles fantastic, with the first turn of the key, on the coldest day. Better then my TDI. I do allow the motor to warm before I drive off, as I do with all my cars.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

If the manufacturer sells the car to customers in colder climates where the oil that the customer might use is enough to cause rough enough cold starting to bend a rod, it is incumbent upon the manufacturer to tell customers not to use such oils or to use a spare car in cold weather. You are painting a picture where the useful operating range of the engine in terms of climates on Earth is not going to include Europe. I lived in Germany from 1959 to 1971. It was one hell of a lot colder there then than it is now in Connecticut. I used Mobil 1 15W-50, which meets the winter oil specs in the manual for the vehicle, and later in its life I used Mobil Delvac 1, 5W40 which also met the requirements (which did not dictate synthetic oil as MB does now).

Getting a Diesel started in sub-zero weather the old days (I have been driving these things since the early 1970's) was quite an accomplishment - and I routinely rolled those early models down a hill and dropped the clutch in third gear to get them started in such weather. Never bent a rod. The 350SD I had NEVER failed to start in the entire time I owned it, even in the winter with the bent rod using the standard starting procedure. In fact, until the rod bent and MB made it clear they were ok leaving me high and dry, I was very, very impressed with the vehicle.

People own these things and start them in all kinds of weather with zero to several glow plugs not working. It is part of the routine, and it is inside the design scope for the engineers designing these machines. It always has been and always will be. Cold weather starting is just a fact of life at the latitudes in Europe, Canada and much of the rest of the world MB serves.

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)