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Old 08-29-2004, 10:43 PM
H-townbenzoboy's Avatar
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350SDL question

I was talking to a church member of mine who drives a 1991 350SDL, and I think she said she has about 118 or 180K miles on it. She told me she keeps bottles of oil in the trunk because sometimes, the oil light will come on, and when it does, she just pops the hood and puts more oil in. Isn't this a symptom of an ailing 3.5L OM603? Excessive oil consumption comes before rod bending, right?

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Old 08-29-2004, 11:15 PM
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Originally Posted by H-townbenzoboy
Isn't this a symptom of an ailing 3.5L OM603? Excessive oil consumption comes before rod bending, right?

This is the symptom. However, the excessive oil consumption comes after the rod has already bent and the cylinder has become ovalized.

She's going to be making quite a few trips between that trunk and that hood.
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Old 08-30-2004, 04:44 AM
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Can also mean an oil leak from any number of gaskets and seals. Turbo seal comes to mind.

95 S420
87 300SDL
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Old 08-30-2004, 06:19 AM
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The oil level light can also become a problem as these cars age. The time delay part of the circuit that allows for momentary level fluctuations from things like cornering or breaking goes south. This can have one trying to keep the level at the full line where most MB diesel thend to use oil. Dave M was working on a repair I can't remember the details, but it likely involves a dried out capacitor.
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1 SDL, 1 D, 1 TD, 1 Mog
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Old 09-05-2004, 07:58 PM
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Now if that doesn't prove that 'rod bending' is chronic and inevitable, I don't know what does!
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Old 09-06-2004, 07:54 AM
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Originally Posted by PeterinCO
Now if that doesn't prove that 'rod bending' is chronic and inevitable, I don't know what does!
Even if "rod bending" were the cause of the oil consumption, and that has not been shown, one example does not prove anything! Even if there were 10 on this forum with proven bent rods, that would not be proof, but would be a good indicator of the likely outcome.
Tony from West Oz.
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Old 09-06-2004, 12:21 PM
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Hi Tony from Down Under. I was trying to be as sarcastic as possible. My immediate mission on this forum to figure out this rod bender thing.

I have heard stories of people replacing diesels at 30 or 40K miles because they NEVER changed the oil. I would have to think that something has SOME bearing on it...
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Old 09-06-2004, 08:13 PM
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You are correct, there is a reason. Unfortunately it is not in MB's best interest to share it with us, so it is highly unlikely we will find out the real reason soon.

For my money, I think it is a combination of things associated with the design and the manufacturing process. I am not a subscriber to the carbon ingestion theory because carbon is a problem that has been available to bend rods on the first of these engines equipped with exhaust gas recirculation, and none of them exhibited the tendency to bend rods before this engine. I believe the rods are flawed by the stack up of design and manufacturing tolerances on dimensions, metallurgy (chemistry and heat treatment) that make rods with certain combinations bad. Others are apparently ok.

Merely thickening them is not always the answer as depending on where the thickening is done, the loads can increase faster than the mechanical properties, leading to a net change in the fringes of when it happens. Jim
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

1971 220D (250,000 miles plus, sold to father-in-law),
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Old 09-06-2004, 09:06 PM
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If the rods were fine why did Mercedes update them? Their was a picture awhile back of an original 350 rod next to an updated one. Their was a big difference.
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Old 09-06-2004, 09:30 PM
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Well, not all of them failed, since mine is still driving, and since the wear metals on the oil anaysis I had taken doesn't show any aluminum, cast iron or lead, I suppose it's still ok.

That doesn't mean it won't fail. look at the space shuttles.
71 220D 169K wrecked
83 240D 118K sweet 4 speed
91 350SDL (one of the 60% good engines) 156K
84 300d (loaner to my sister) 189K
79 300SD (partswagen)
86 420SEL partswagen
70 220d (partswagen)
68 280s GASSER!!! under construction now
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93 300d 2.5 turbo 168K wife's car
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Old 09-07-2004, 09:04 AM
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91 350 Sdl

Mine has 234,000 on it with no oil consumption or rods bent. It is the best diesel car I have ever driven.
91 350 SDL
91 300 E
85 300 D (sold)
79 300 CD (sold)
91 300 CE
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Old 09-07-2004, 03:56 PM
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If oil consumption continually increases on an OM603, it's more likely to be the bottom end failure than anything else. Normal oil consumption for that engine is about one quart per 4000-6000 miles. At 2000 miles/qt, something ain't right. At 1000, start budgeting for a short block. At 500/qt or worse, you're on seriously borrowed time, and other symptoms may appear - low power, smoking, etc.

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