1. A Clogged Positive Crankcase Ventilation (PCV) Valve
The PCV valve is connected to an air intake housing via an often-rubber vacuum hose used to provide a vacuum release inside the engine’s crankcase. This component is typically installed on top of a cylinder head valve cover, where pressure flows from the engine’s bottom half, through the cylinder heads, and exits into the air intake. The PCV valve is similar to an engine oil filter in that it eventually becomes clogged with excessive debris (in this case — engine oil) and should be replaced as recommended by your vehicle’s manufacturer. If the PCV valve is not replaced as recommended, excessive oil will blow through the PCV valve and enter the air intake system.
2. Worn Piston Rings
A second potential source of engine oil leaking into the air filter housing is due to worn piston rings. The piston rings are installed on the outer edge of the pistons inside the combustion chamber. The rings are intended to create a combustion ratio and permit small amounts of engine oil to continue lubricating the inner combustion chamber during each piston stroke. When rings wear out, they loosen and can cause oil ‘blow-by’ — usually displayed by blue smoke coming from the car’s tailpipe while driving. In the early stages of worn piston rings, excessive oil blow-by can cause excessive pressure to build inside the crankcase, which sends more oil through the PCV valve and eventually into the air intake, as stated above.
3. Clogged Oil Passages
The final possible reason engine oil will find its way into the air intake system and eventually clog the air filter is due to clogged oil passages. This symptom usually occurs when the engine oil and filter have not been replaced as recommended. It is caused by excessive carbon deposits or engine sludge developing inside the crankcase. When the oil does not flow efficiently, excessive engine oil pressure will be created and cause extra oil to push through the PCV valve and into the air intake.
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