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Steve
Steve, Auto Service Technician
Category: Car
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Experience:  25+ yrs experience as a professional working technician; ASE L1 master technician
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85 Mercedes 300D suddenly blows blue smoke and runs rough!

Customer Question

What happened to my '85 Mercedes 300D Turbo Diesel which was running great? Noticed rough idle at stop sign. Checked engine and noticed a little bit of blue smoke coming from rear of block. Air filter chamber had more oil than usual at bottom. Formerly smokeless exhaust now has blue smoke. Oil level down about two quarts. Also noticed some coagulated oil on block sides and all around valve cover where it meets cylinder head. Cannot tell if additional oil is coming from where cylinder head meets block. Possible problems and cures?
Can I drive car to repair facility 2 mi away or do I need to tow?
Submitted: 11 years ago.
Category: Car
Expert:  Steve replied 11 years ago.

If the problem appeared suddenly, the most likely cause is a turbocharger failure. Engine oil is pumped to the turbocharger to lubricate the bearings in the turbo; if an oil seal fails internally it can cause oil under pressure to leak into the inlet or outlet sides of the turbo, resulting in blue smoke from burning oil (exhaust side oil leakage) or working into the air box or into the intake manifold of the engine (intake side leakage, also resulting in oil being burned making blue smoke).


I would suggest having the car towed, so as to not damage any other components that are not already affected, or to not risk losing excessive oil and causing internal engine damage also.

Customer: replied 11 years ago.
Reply to Steve7654's Post: I appreciate your concern for possible turbo failure and the towing suggestion to avoid further complications.

The symptoms are not necessarily "sudden"; my window was open and I heard rather than felt the rough idle-which prompted the engine inspection. This may have been going on for awhile.

This assessment does not take into account the coagulated oil or exhaust smoke at the rear of the block.

I probably should have included more details; the turbo was supposedly checked out at the last oil change (4000mi ago) and while it could be an issue, I am more inclined to believe there are other problems involved.

Regards, ml
Expert:  Steve replied 11 years ago.

A failed turbocharger can leak oil externally; it is extremely difficult to be able to diagnose every possible oil leak on the engine without being able to see the vehicle to follow the oil back to it's source. It is possible you could be seeing oil from the turbo failure, or it could indicate another smaller secondary leak from somewhere else.


I have very high confidence in the turbocharger failure diagnosis I have presented to you; it is a classic set of symptoms related to turbo failure. As far as checking the turvbocharger 4000 miles ago, the only checking that is possible to do in that regard is to check to see that it is operating. All of the oil seals in the unit are contained internally and inspection of them is not possible without removing the unit from the vehicle and disassembling it for inspection (not something thatis routinely done, even for repair; the standard repair is to install a factory new or reman unit). therrefore, inspoecting it 4,000 miles ago would likely have shown no signs of a problem if it was operational at that time....


I am 99% sure that you have a failed turbocharger here; having it checked by a technician I am sure will confirm the diagnosis. At any rate, it is very unlikely to be something you will want to attempt to repair in your driveway, so taking it in to a tech for diagnosis seems like the most logical course of action in any case. I thought you were looking for possible failures in your question, to give you some idea whether the technician doing the diagnosis is on the right track or not... It is practically impossible to provide a 100% detailed thorough diagnosis and repair procedure on a vehicle through a written description, not being able to see or test the vehicle in person.


I hope my answer has been helpful, and I am very confident that it is as accurate as humanly possible under the circumstances. If you find it helpful, and think the time I have invested in trying to help you out is worth the $10 you posted, clicking my accept button would be most appreciated; we specialists receive no compensation whatsoever other than a small percentage of the amount paid for our accepted answers. If I can be of any further assistance here, please let me know; I want my customers to be satisfied with their experience here! Thanks...

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