I have a friend who owns a 1993 300SD with the OM603.971 motor and he is trying to figure out an unusual problem. When the engine is started up after the vehicle has been sitting unused for several days it smokes. If the 300SD is driven everyday it doesn't smoke on startup. I initially suspected that it might be bad valve stem seals, but the head has new valve stem seals along with a new head gasket. The 300SD has about 130K miles on it I believe. He is also pretty certain that the smoke it produces on startup is caused by oil, as opposed to being diesel smoke. Does anyone have any ideas on what might be causing this problem?

Thanks in advance.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

Being a 603.971 it can only be bent rods

Pretty obvious from the smell whether it's unburned fuel or oil... or coolant

The best of us (aka gsxr) have been victims of bad or improperly installed valve seals.

If there's an accumulation of grime or wet oil in the aread around the #1 exhaust runner, it could be a bad head gasket. The gasket doesn't do a good job of sealing the oil feed for the head. Not for very long, anyway. Oil seeps past the gasket externally and to the #1 cylinder. Why it only manifests after sitting for a few days is beyond me.

Sixto
87 300D

If it were slow leakage into a cylinder or cylinders the time frame might be signifigant. I think nothing of a good diesel sitting for six months smoking heavy on the first startup if it occurs. Only a few days is another kettle of fish.
Is the overall average amount of base oil consumption known? Is the initial restart after several days rough or smooth in nature? Thats in comparison to the starts when in everyday service.

I was able to get a bit more info on the problem. The actual mileage is about 170K, not 130K as I originally believed. The engine runs smooth, and the smoke only occurs when engine is revved above idle speeds. The updated head gasket was installed at the same time the valve job on the head was completed. Apparently the 300SD sat unused for about a year until my friend purchased it, and then did a valve job on it. The engine runs fine except for the smoke that only occurs on startup after it has been sitting for a few days. My friend is beginning to think it may be something related to the rings, but it is kind of unusual or problems to occur with the rings at only 170K, and only after the vehicle has been sitting for a few days unused. The problem doesn't manifest itself otherwise.

Thanks for all of the ideas so far.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

Many times the 3.5L engine will have bent rods and either an ovalling cylinder or crooked, worn pistons, but still run remarkably well. One sign to look for while the head is off is "tipped" pistons. This seems to be the key indicator of the more serious issues to come. Can you talk with the mechanic that did the head gasket?

Actually the friend that owns the 1993 300SD with the OM603.971 is a factory trained Mercedes-Benz Technician. He performed the head gasket replacement himself, and had a valve job done at the same time. He's kind of stumped as to the cause of the oil burning on startup that only occurs after the 300SD has been sitting for several days. He did mention the cylinder walls looked good with the crosshatching still visible. He's also familiar with the rod bending syndrome of the 3.5L OM603s motors as well. I would suspect that he checked the pistons in their bores when the head was off but I'll confirm that. I'll also see how much (if any) oil is being burned. I just was trying to see if anyone had additional ideas.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

* It's not that easy to differentiate oil-related exhaust smoke from diesel combustion on acceleration (most noticeable) or cruising (less noticeable) even if you're watching from a car following behind the smoker.
* You've probably checked the turbo for oil leakage into the intake. I just recently had an OM603 turbo rebuilt. The new seal wasn't installed right, and I didn't find out until I went for a test drive. The smoke was a black cloud, not unlike the smoke from a fuel problem. Then there's the ALDI unit. If someone reshimmed it or adjusted it, to gain some performance, maybe they went too far (rich) or didn't reinstall the unit right.
* Are there any signs that the engine might have been overheated? New radiator, hoses, thermostat. A compression test would eliminate the bent rod scenario, but ring damage from serious overheating could cause your progressive smoking problem on acceleration and cruising (i.e. off idle).

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ASE Master Tech
Quality Enterprises
Mercedes Svc. & Restoration
Sheridan, IN
317.769.3536

Steve,

I recently had a similar problem with a 98 e300 turbodiesel. The car I am working on had a oil leak and oil in the injector wells. Some of the oil would then seep into the prechambers causing blue smoke during warmup.

After quite a bit of disassembly and assembly, I pulled the cam towers and discovered that the seals that go on top of the head and under the cam towers were never installed. I am not sure if your motor has these seals but it might be worth a look. It was not all that much work to pull the cams and cam towers.

John

I ran a Diesel Rabbit for 13 years and learned a few things that may be applicable here. I would check the glow plug on each cylinder to see that they are operating. As diesels need a bright heat source initially to start a non-functional one would cause these symptoms and would go away shortly after start up as the compression quickly builds up enough heat to sustain the ignition of the diesel fuel. It would not explain the fact of only occurring after a few days of non-use. I also assume that the "over engineering" aspect of Mercedes probably would detect and alert the operator of a non-functional glow plug. Rabbit's diesels were the most simple of basic diesel engines - 4 high compression cylinders and injectors an injection pump fuel filter and glow plugs. Those are the basics and besides oil and good 590 CC Amp battery that is all that is required for a good running rabbit engine.