Rod Bender questions

[Dwayne1m]

I'm thinking about buying a 1990 350 SDL. It has 360,000 miles on it and is the original engine. I'm new to Mercedes so I'm trying to learn as much as I can about this "rod bending" issue before I take the plunge. I hope some of you here can point me in the right direction. I've read that if it hasn't bent any rods to this point it should be "OK", correct or not? Does this engine block use cylinder liners or not? I've also read mixed reviews of the head on the car. Can someone give me the part numbers for the preferred & not preferred engine, head, transmission or any other vital part. A side question....have "new" rods solved the bending problem and did anyone ever solve the mystery?

Thanks, Dwayne

[compu_85]

If the car has that many miles on it the engine is not one of the "bad" ones. It would have been dead around 120,000 miles.

New rods are available that are stronger, as are cylinder sleeves to correct a ruined block. (Normally there are no sleeves)

-Jason

[t walgamuth]

The idea that there are good ones and bad ones does not necessarily seem correct to me.

Any 3.5 motor no matter how many miles on it would seem to be a candidate for a bent rod to me.

If the car is in excellent shape I would only buy it if I could buy the car and install a good used 3.0 liter block and be ok on the total investment.

The 3.5 heads are not the ones prone to cracking. The earlier heads from the 3.0 are the crackers.

[MTUpower]

IIRC non USA models did not have these problems- it relates to poorer quality USA fuel and city driving. Many, many of the 3.5's are driven until the body gives out- not the engine.

[JimmyL]

That is getting to the mileage where any engine starts to be likely to fail soon enough..............
I'm always amazed when I hear about rod-benders making it to that mileage. Couldn't you just whip the arse of those weasily engineers at MB who know what the issue was yet won't let the cat out of the bag! {yes, I realize that the just can't}

[Dwayne1m]

The body is in very good shape, otherwise I would not even consider buying this car. If I would switch it over to a 3.0, what would be involved in that? Are the transmissions interchangeable? Correct me if I'm wrong but isn't the 3.0 a 5 cylinder and the 3.5 a 6 cylinder? Just a side thought here but it was always my understanding that MB had an outstanding mechanical reputation. After surfing some of the topics I find that reputation is not accurate. What is the advantage for paying more for repairs and parts if the results are the same as other car manufacturers?

[BenzDiesel]

Originally Posted by MTUpower

IIRC non USA models did not have these problems- it relates to poorer quality USA fuel and city driving. Many, many of the 3.5's are driven until the body gives out- not the engine.

This is a total myth. The poor quality is in the car, not in USA fuel. Daimler has great engineers who were responsible for building the 3.0 and 3.5 engines. However, an engineer can draw up the blue prints to send a man to Pluto, but if somebody attempt to use cardboard and newspaper or even stronger, plastic, to get to Pluto; you can bet on not making it no matter how great and accurate and ingeniuos the designs are.

The USA fuel myth is like superstitions, where when you don't know for sure; you can just about believe anything.

Daimler doesn't know the causes for the failures itself because they sublet the building of the cars to such a sever degree that noboby knows how all of the parts fit together and that is by design. No good intentioned builder of cars would put a $2.00 part on the car in critital areas that will make the car inoperable if the $2.00 part fails, espcially on a $100,000.00 car. Daimler could have used platinum instead of many of these $2.00 parts and still made money, especially in USA models loaded with $2.00 parts.

BenzDiesel

[duxthe1]

That I am aware of, there are a few reasons for bent rods in those engines. About ten years ago I got wind from a dealer that the reason that a lot of the later produced 3.5s bent rods is b/c M/B actually started using a lighter weight rod in a effort to improve efficiency. Those lighter weight rods just weren't up to the task of taking the pounding that the heavier rods would. If caught beofre further damage those engines could be torn down and be rebuilt using the older heavyweight rods and be fine.

The other common occurance is for coolant to make it's way into the cylinder causing a rod to bend. That isn't so much a 3.5 problem but a 603 problem. If a small amount of coolant can make its way into the cyl it will erode the block and head due to what I'd call coolant detonation. If enough coolant makes its way into the cyl, bye bye rod(s)

[MTUpower]

Originally Posted by BenzDiesel

This is a total myth. l

Really? Are you sure?
Do you have proof this a myth?

[JimmyL]

Originally Posted by MTUpower

Really? Are you sure?
Do you have proof this a myth?

William, sometimes you "think" somebody may be dumb as a box of rocks, then some folks go out of their way to prove they are.

http://www.peachparts.com/shopforum/showthread.php?t=249305&page=12

Start at post 173 and see if you can spot the rocket scientist.......

My new forum anthrax......

[Skippy]

After 360,000 miles without a bent rod, I'd say it's unlikely to bend one now. However the entire drivetrain is likely to be worn out or getting close to it. Buy it for $500 if you can and drive it til it quits.

[sixto]

There are two 3.0 Diesel engines common in the US - the through '85 5 cylinder OM617 and from '86 6 cylinder OM603.96. The 603.96 was bored and stroked to make the 90-95 3.5 603.97. The 603.96 block and reciprocating assembly is a direct swap for the 603.97. I'm pretty sure a .96 oil filter housing and oil pan can be used in a .970 host, but not in a .971 host. In fact you can drop a complete .961 engine pretty much as is into a 90-91 350SD/L but you might be trading propensity to bend rods for propensity to develop head cracks. Consider using the later .97 head if the .96 has the original head if your hands are already dirty.

I'd be concerned about how much suspension work is needed in a 360K miles 126. That could cost more than an engine swap. Tranny too.

Sixto
87 300D

[MTUpower]

Originally Posted by JimmyL

William, sometimes you "think" somebody may be ...

Wow, you hit the motherlode with this one.

[BenzDiesel]

Originally Posted by MTUpower

Really? Are you sure?
Do you have proof this a myth?

However, I don't have anything to prove to anybody. This forum has some great information and some really, really bad information that looks and sounds good, but nevertheless is bad. The reader has to be skeptical and try to pick out the good stuff and throw out the fluff, which there is a whole lot of. It is one thing for certain that I know and that is: you are not going to fix your Daimler car using information based on the popularity (a popularity contest) of the poster who said it if what is said is false information or the poster is German and has an ulterior motive to think these cars are more than they are. Chevrolet needs to hire these German engineers (some of them) and combine great engineering with quality material product, except for body parts that can't stand up to rust in Detroit. Plus, 50% of the battle would be won if the $2.00 parts Daimler frequently uses in USA cars were taken out of these cars made by Chevrolet assisted by a few German engineers tired of their great work of designing being sabatoged with faults such as cracked heads and bent rods and any other fault a critical $2.00 part can cause.

BenzDiesel

[MTUpower]

Originally Posted by BenzDiesel

and throw out the fluff, which there is a whole lot of.

mean like this post? I'll throw this out as you have proved there are really dumb Americans.

Originally Posted by BenzDiesel

I don't have anything to prove to anybody.
No wonder they call us "DUMB" Americans.
What's the reward for losing a WORLD WAR II?
This ain't Saudi Arabia!!
I know Italy is in there too, but Italy knows how to behave as a defeated country of a World War II.