: Blow-by is caused by combustion pressure gasses getting past the piston rings ("blowing-by" - thus the term blow by) <p>This is a normal occurrence as the seal between the rings and cylinder wall is never 100%. <p>As the combustion gasses blow-by the rings and cylinder wall, it picks up oil mist from the crankcase of the engine. <p>All modern engines have what is called positive crankcase ventilation (PCV). This is basically a vacuum which is drawn through the crankcase and entered into the engine intake. This ventilation picks up the hydrocarbons and other waste gasses from combustion, along with oil in suspended in a mist form inside the crankcase. <p>As a result of this ventilation , blow-by residue in the form of dirty oil can and will accumulate in the area of the intake. (As you are seeing around your air filter)<p>PCV is a beneficial cleansing action which prolongs engine life tremendously. ( the PCV Valve is a common tune up part that regulates the process) <p>I hope this helps...<p>note: Obviously excessive blow-by is an indication of worn rings and or cylinders. This is usually accompanied by a smoky blue exhaust.<p><p><p><p><p>: 18/03/01<p>I have a 22 year old 300TD.. Today I was told that I have a bit of oil in the area where the Aire Filter is.<br>Does anyone know what may cause this? I have been told not to worry about this matter. Should I worry? <br>Any feed back appreciated..<br> Leo.<p><br>31 March, 2001<p>Will, Thank You very very much for your response on my question about Engine Blow By... I took my car into The Mercedez Dealer Ship for a check up and a compression check.. They said the car was fine...Thank Again... <p>
