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I have a Mercedes B class diesel 2010. I have had it since August 2015 from a dealer who serviced it, and everything is running fine. I have noticed a warning saying drop oil level, so I measured the oil and it's just over the full dipstick mark. I've been getting this warning for 2 weeks now, do have I anything to worry about? Will the problem go away on its own or do I need to do anything?

I have checked the dipstick and the oil is just over the top mark ,the oil looks ok (black) no foam etc and no smoke from exhaust the warning sign comes on when on long drives (on rare occasions)

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Unless you recently added oil or had it serviced, I would be concerned. I would wonder what is raising the oil level. Do you have any signs of engine oil mixing with coolant? Does the oil have a tan colored foamy appearance? This could be an indication of coolant leaking into the crankcase.

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    The really dumb reason would be that somebody else checked the oil, topped it up, and overfilled it. But if you are sure that isn't the case, the oil level increasing on its own definitely needs investigating to find out what is getting into the oil system. Another possibility is that the indicator has recalibrated itself. That also needs investigating, because you don't know if the low oil level indicator has also gone out of specification, and you don't want to find that out by wrecking the engine some time in the future!
    – alephzero
    Mar 14, 2016 at 21:58
  • @alephzero well, he says that it's over the full dipstick mark, so it makes sense that the sensor reacted. The question is how and when it increased.
    – I have no idea what I'm doing
    Mar 15, 2016 at 10:11
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Too much oil can block flow passages, cause overheating due to foaming, and other problems. If it's only a little bit high, you probably haven't caused major damage. But I'd drain a bit out as soon as possible.

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I'm 90% sure it's a problem with DPF filter. Problem with increasing oil level is quite common with all modern diesel engines when you rarely drive out of city. Also, after some mileage it simply won't work properly anymore and needs to be changed for a new one.

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  • DPFs really are problematic on city cars, but it would be great if you explain how you made this connection between a high oil level warning and a clogged DPF.
    – I have no idea what I'm doing
    Mar 15, 2016 at 13:33
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It could be diesel or coolant if it's not just too much oil in there from the beginning.

Apart from the other answers about foaming and coolant in the oil, you should also be aware of runaway, which is when a diesel starts running of its crankcase contents or exterior gases instead of diesel from the injectors. This can happen if crankcase oil is pulled into the engine through the crankcase ventilation or a bad turbo. This is more likely to happen if there is a lot of diesel in the oil and if the level is too high.

Turning the key won't help if this is the case, so I would drain the excess oil ASAP and see if the level continues to rise. That would suggest that further investigation is needed.

Pretty nice summary of the effect: http://www.autoevolution.com/news/heres-how-you-quickly-stop-a-runaway-diesel-video-87344.html

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