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Hey people! I was changing the air filter on my '80 240D and when i got the old filter out of there, i noticed it looked sort of a little oily on one side, just a little bit. Then i looked down into the intake manifold and i saw some black liquid what looked a lot like used engine oil, so i am not exactly sure if it was engine oil, but nevertheless, it was some sort of black funk. Do you guys think this is something i need to check out or this is something completely normal? I was thinking maybe some valve was not properly adjusted and when the engine went to compress the fuel, there was a little gap and because of very high compression pressure, some of the fuel mixture may have gotten out of the combustion chamber and into the intake manifold, and that's when i saw it. This is what comes to my mind, but let me know if you can what you think!!!Thanks a bunch!
 

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Due to the high compression, diesels are famous for blow-by. You might have notice that the oil was just below where the tube on top of the air cleaner was. This tube is used to burn any blow-by so it doen't get in the air. Don't know how long it has been since you last looked there but expect some oil when you do look. This is normal.
 

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What exactly is blow-by? Is that pretty much what i thought the oil came from, i.e when pistons compress the fuel mixture, some of that mixture gets into the intake manifold? This was the first time i looked directly into the intake manifold. I did that because i noticed that the air filter compartment was a little oily on top on the inner filter side, which made me question if that was an okay type of thing to happen. Thanks [:)]
 
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yeah, the breather system for the crankcase is famous for letting the oil recondense and collect in the turbo and manifold. try "Seafoam" brand cleaner, the type that comes in a aerosol can. it is the same as the liquid kind u use in the tank, just in aerosol spray for fogging down ur intake. unlike almost all other sprays, its not "super combustible", and is entirely safe for diesel motors. i spray an entire can through my motor directly into the open turbo like once a month, and it keeps everything quite clean. is found at autozone here, probably most parts places have it.
 
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blowby occurs when the imperctly shaped natural "crude" oil molecules dont stick together when extremely compressed by the piston rings going up and down in the cylinders. they "tear" apart from one another and allow small amounts of pressure to get let past them, which lets this gas into ur crankcase. all motors do it, its unavoidable. however it can be reduce to almost none by using a good 100 percent synthetic diesel oil, where all molecules are exactly identically shaped and sized, which creates a super strong film strenght, which keeps the film from "tearing" apart, thus severely rearding blowby, and due to this ur compression is slightly higher. (closer to original levels, like when the motor was brand new)
 

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Simply put, blow-by is indicative of engine wear. The more blow-by, the more engine wear. As the piston cylinder wears and rings weaken, more compressed air created during the engine compression stroke leaks by, creating pressure in the crankcase. The pressure is relieved through the breather pipe on the valve cover into the intake manifold, and carries oil with it as it exits. You will notice more oil use as the blow-by increases. As long as the engine runs fine, don't worry about it. Just check your air filter often to make sure it does not become soaked with oil.
 

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AMSOIL300CDT - 3/11/2005 10:00 AM

yeah, the breather system for the crankcase is famous for letting the oil recondense and collect in the turbo and manifold. try "Seafoam" brand cleaner, the type that comes in a aerosol can. it is the same as the liquid kind u use in the tank, just in aerosol spray for fogging down ur intake. unlike almost all other sprays, its not "super combustible", and is entirely safe for diesel motors. i spray an entire can through my motor directly into the open turbo like once a month, and it keeps everything quite clean. is found at autozone here, probably most parts places have it.
First off the guy has a 240D- which does not have a turbo. Secondly, the oil in the intake comes from the valve cover breather and into a oil seperator that may or may not be located inside the air filter housing depending on the model and year. " This tube is used to burn any blow-by so it doen't get in the air." The tube does not burn the oil, it transports both the gas and liquid to the oil seperator which seperates the gas(air) from the liquid(oil). Take a look under the air filter housing- you'll see a tube leading to the crankcase- which is where the liquid oil is returned to the system. The gas from the valve cover is released into the intake.
You also have a EGR, which is short for exhaust gas recirculation, which at lower RPM's puts some of the exhaust back into the intake to reduce emissions. Between the oil seperator and the EGR your OM616 and OM617 engines will over time accumulate sludge in the intake. No one has shown conclusively that this is detrimental to performance or engine longevity, but it sure is ugly, and it is generally thought that cleaning it up will do some good somehow.
BTW Blowby is the result of the compression of the fuel and air, which passes between the piston and the cylinder wall into the crankcase. All diesel engines have blowby, even brand new ones, which is why there is a crankcase breather. Using sythetic oil will not stop blowby. Where you thought that one up is sure not at diesel engineering school- most likely some Amsoil propaganda. The crankcase breather system is not there to take care of blowby down the road after 50 thousand or 100 thousand miles when the engine is older- it's working from day one.
 
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