S 600 blown engine
 

Posting this to several forums as i'm a bit frantic. My 1995 S600 with 55K miles began to act a bit more sluggish right out of Boise, and somewhat later there was increased color (dark) to the exhaust when downshifting into passing gear. Took it to the dealership, and they swapped computers, air mass meters and o2 sensors and found tht the left bank of cylinders was pumping way too much fuel. None of the above fixes helped and
the final diagnosis was a crumbled wire harness. Cost to fix, $6K. Sad song, but gets worse. He thinks the engine may have been permanently damaged by too rich fuel flow and feels the best bet would be a rebuilt engine at $28K. Worth of vehicle is 30-40K and it is in excellent condition, interior is showroom and all the goodies work. Min paint chips. Has anyone ever heard of this problem with blown V-12's? I have written MB more of less offering to pay for the harness, but if the engine is gone I hope they would help with that. This is a known design defect, but apparently no technical bulletin issued as I checked with my shop the day I got the car and made sure everything was kosher. Unfortunately, i was not the car's first owner. Any thoughts?

With too much fuel(rich) all you do is waste gas and maybe damage your catalytic convertors. Only if your engine was running lean could you have some damage. I would get a compression/leak down test at another repair facility and go from there before spending any more money.

s 600 blown engine
 

Thanks. I guess the mechanic thought that all the extra fuel "washed all the oil off the pistons and caused the rings to burn" I don't want to pretend to be any sort of mechanic these days, but apparently the pistons are silicon lined and the valves are chrome, so they should be pretty resilient. I thought about the catalytic converters, though. Someone said that we should have smelled something burning, and we didn't so hopfully it was a brief enough event that they weren't damaged.

Shouldn't there be a 'check engine' light warning of these problems?

The engine damage part of your story sounds fishey to me. I have never heard of a "too rich" mixture causing any engine damage. It will cause carbon build up, but damage? I think not. If the fuel was so rich as to "wash all the oil off the pistons and caused the rings to burn" I doubt it would run at all. You would have to have a serious flooding with all that fuel and things dont ignite when there is that much fuel.

I would replace the wiring harness first, and then test the engine and see what condition it is in. One step at a time.

Well, I have indeed heard of motors
 

damaged by excess unatomized fuel washing down the cylinder walls and causing the rings to score them deeply, and that was with cast iron blocks -- with an aluminum-silicon block, I would expect the problem to be worse rather than better. On the other hand, the damage hasn't yet been proven to exist; even if there is some, it may be very light and go away again after a long "break-in" period -- I've seen that happen, too, albeit on a farm tractor which flooded its intake system because of a stuck carburator float.

If it were really pouring in the fuel, washing down cylinder walls and diluting the oil, it is indeed possible that there is damage.

Best of luck,

Has the car been dealer maintained its whole life?....if so..I would think that the dealer would go to bat with you with the MB zone rep and get you some assitance....at 55K miles MB should be willing to contribute......PROVIDED that the car has an good service history...which usually means only a dealer worked on it


Warren
1992 300SD 142K
Columbus Ohio

"He thinks the engine may have been permanently damaged by too rich fuel flow and feels the best bet would be a rebuilt engine at $28K. "

It's a good bet all right - for him.

He wants you to spend $28K without even running the standard checks like compression and leak down, looking at the cylinder bores, testing the oil for fuel contamination ...

I would get the car to another mechanic as quickly as possible. And I would certainly raise hell with Mercedes about their flagship model needing a wiring harness at 55K miles.

Good luck.

I read it as he was driving the car when the "washing" occured. So the engine was running. It had to be firing. I find it hard to believe that he had so much fuel as to wash the cylinder walls while driving the car. Can you get enough liquid fuel in a combustion chamber while it is running to wash the oil away?

Educate me.

I love this board, I learn new things all the time.

Jerry S,

I agree with most who have noted the likelihood of severe damage should be low. I am having a hard time believing the fuel injection system is capable of passing enough gasoline into the cylinders to wash them and remove the lubricant film. At least not without having the check engine light come on, and make the engine run so poorly the car would not move.

As I recall when MB introduced the aluminum alloy block with the embedded silicon crystals, they installed a boroscope or fiberscope at every dealership and the bore conditions were visually recorded and monitored. I also believe such an examination, along with the usual compression tests and leak down tests should be performed to assess whether or not any noted visual indications of wear are more than visually apparent surface conditions. Looking at a machined surface under high magnification can be difficult to understand without some additional information. Some stuff looks really bad close up, but is actually normal.

The original idea behind the aluminum alloy MB selected was to bore the cylinders, then acid etch a very small amount of aluminum away to have the rings ride on the polished bits of silicon that were now protruding slightly. The wear characteristics of the silicon were (are) much better than those of the aluminum and intended to be superior to those of typical sleeves or sleeveless iron based castings. In your case the rings may have suffered if indeed the oil film was washed away, or I guess if the material got hot enough you might have ripped the silicon crystals out of the aluminum (which is what MB was visually inspecting the engines for in the intial introduction period). Anyway, you cannot see the rings so you really do need to have the other tests done.

I would be reluctant to give in on the wiring harness at 55,000 miles. That is barely out of the 100% warranty period, and it is a major defect in either workmanship or design, unless there is some sign of other damage, in which case you might get your insurance company to kick in for the repair (like rodent damage or road debris or something).

Good luck, Jim

Yes, I believe you can get this much fuel while rolling down the road. There is a point where it would be so much fuel that it would be more than the minimum combustion chamber volume would be exceeded causing uncompressable liquid causing serious damage. But, I think it's safe to say that the injectors could not flow this volume even if held wide open constantly.

An excessively rich condition would NOT be a healthy thing.

Have a great day,

Oil analysis would tell % of gasoline in oil and give a good idea of the "oil washing". Needs a lot of tests; compresssion, leak down, boroscope, wire trace, before condemning the engine. I think it's worth contacting a vehicle transport company and getting it out of there and off to Continental Imports or MB Autowerks or Bergworks. Best $1000. you'll spend on it. eBay sellers transport cars cross-country all the time; one of them will tell you who to use for transport of a high end vehicle.

Yep.

Based on the amount of money you're likely to spend (or not spend) on the car, I think you'd be better off taking it to one of the indpendent techs that Moderate the site, such as Steve Brotherton's shop, Continental Imports in Florida, Donnie's shop in Georgia, MB Autowerks, or even the shop that Ashman recommends highly, Mr. MB Motors in Tarzana, CA.

Oil analysis
 

would show not only gas in the oil, but most importantly abnormally high metal content if the engine was damaged.
I use Blackstone Lab for my cars. It is only $17.
For your reference the last Mobil 1 15w50 oil analysis results from 92 600SEL with 117k miles on V12 engine:
Aluminum 3
Chromium 3
Iron 8
Copper 3
Lead 0
Tin 1