Adamkn

Hello, I need your help, I notoced that my 2009 w204 with om646 emgine make cloud of blue/white smoke whene downshifting in low speeds. I have no smoke on cold start and it make no smoke on hight speed . The coolant level is ok also oil.it does only whene slowing. Help please , This is my first Mercedes I use to drive VW cars and I don't know anything about it.

dol4er

Blue smoke means that the engine is burning oil...

Adamkn

Thank your for your answer , I'll keep cheking my engine oil level, but untill now I didn't notice any change . I'm wandering why it happened only whene I slowdown? It seems like something get stuck as it disaper once I push the gas up. EGR? Catalyst converter?

bowenxue98

No, I think blue smoke means there's a head gasket leak and the engine is burning coolant. You should get it checked out ASAP as that is a major problem and you should have a check engine light.

ronbutchart

In my experience smoke while downshifting could be from worn valve-guides which allows oil to get into the combustion chamber when the engine vacuum is high.

Adamkn

I'v had a faulty gasket in a Peugeot car, the car is not overheating and there is not cooler probleme. I've put the car on stressed in the highway white no problem.

Adamkn

I think that is the issue. As it happene only whene I slow down . I feel like something is jammed as it disappear once I accelerate . Do you have any idea how to solve that ,? I feel ashamed a very time I live a cloud of smoke behind me .
update: I Googled it, it hope it's not the valve-guide as it looks pretty serious!!!

gamma300C

...how many miles/KM on the engine ? I would put worn turbo shaft seal high on my list, faulty injector pump and/or lift pump (which allows engine oil and diesel fuel admixture, faulty injectors (they're squirting in too much fuel, and the excess is dribbling down the bores into the sump)., wrong grade of oil (which is too thin for this type of engine).

Adamkn

it has around 140000km. The previous owner used it only in the city. Would you please tell me if there is any symptoms for that? The car start with no problem in the morning, no smoke, no noise. For the oil, I think it has 10w40 in it .

ItalianJoe1

On a turbo vehicle, like your diesel, the smoke is usually from worn turbo seals. Leaky valve guides will allow the oil to soak down overnight and the vehicle will smoke heavily on startup. The turbo seals have pressure against them when working, but when coasting the vacuum allows the oil to run past.

I'd pull the inlet and check for shaft play, and plan for a turbo rebuild if you find any.

ronbutchart

Gamma300c and ItalianJoe1 have good ideas and more experience than me on turbo systems. I think we all agree that the likely issue is oil in the combustion chambers (too much fuel used to make black smoke and oil would be white but then I could be showing my age again!). There might be a fair amount of disassembly needed to figure out exactly what has failed/worn out.

Adamkn

The car doesn't make any smoke in the morning. I 'll go check the shaft play. Well , I must find it first. That engine is completely unknown for me. Just switched from a passat 5 days ago.

the smoke is more clear blue than black. I agree with you, I'm trying for pin point the problem as I don't want to dissamble all the engine for that.

bowenxue98

You should take a video of the problem that way its easier for us to see.

Adamkn

It happen only when I'm driving. I'll try to fix a cam on the rear window to get it for you ..
I also noticed that I have some oil vapor around this area

ItalianJoe1

That's part of your PCV system, which was gonna be my second suggestion. If you aren't getting good crankcase vapor control, it can push oil into the intake while driving. There shouldn't be any visible oil vapor, check for cracked hoses or broken parts, a lot of those systems are plastic and get fragile with age. I'm not too familiar with those engines, I never see them, but the basic principles apply.

dol4er

Oh, 10w40 is a totally wrong oil, you should drain it immediately. You need to use the right oil with any car. Every car manufacturer has its own standards and approved oils.

Adamkn

Quick update: I tested the valve guide by driving the car down a hill in low gear and hard acceleration after. No smoke.On the other hand whene I started the car this morning I got smoke immediately after a took off.. heeeelp!!
I managd to get a video of the car making smoke

https://youtu.be/-QnCr2ZbPho

Adamkn

Now I have smoke whene I start driving in the morning.

ItalianJoe1

Have you checked the turbo yet? Have you addressed the PCV system leaks?

dol4er

Well, these cars can be diagnosed perfectly well, however not over the internet but with a STAR diagnosis. I think it is high time for you to visit your dealer.

Adamkn

The PCV is not cracked. The turbo will be checked tomorrow. But I'v found some condensation on the area between the diesel filtrer and the egr.



I dont know if this is normal?

alecmascot

I have the same engine as you.
The little cap on the cam cover is the oil separator. Mine was not seated properly and released a bit of oil mist.
That assembly is part of the cam cover and is not available separately. I was able to remove the cap and seal the diaphragm inside with high-temp silicon. If you break it it will cost $$$ to fix as the injectors have to come out.
Be careful not to become paranoid. These engines are very long lived if maintained regularly.

Adamkn

thank you very much, I think I'm becoming paranoid with that, I'm trying to calme down and learn to ignore it. I tried to reset the transmission. No more smoke until now ( juste a little but normal).