Engine oil should never be found in the air filter. Depending on how it got there, minor or major repairs may be required.
The air filter is made to capture debris, dirt, and other contaminants — but not the engine oil. Occasionally, when a local service mechanic changes an air filter, the technician will notice that engine oil has been found; either inside the air filter housing or embedded inside the used filter. While oil finding its way into the air filter is not greatly a sign of catastrophic engine failure, it should definitely not be neglected. Let’s check the top 3 reasons oil finds its way into the air filter in the first place.
- A Clogged Positive Crankcase Ventilation (PCV) Valve
The PCV valve is always connected to an air intake housing through an often-rubber vacuum hose used to offer a vacuum release inside the engine’s crankcase. This component is typically mounted on top of a cylinder head valve cover, where pressure moves from the engine’s bottom half, through the cylinder heads, and exits into the air intake. The PCV valve is about the same thing to an engine oil filter in that it eventually gets clogged with excessive debris (in this case — engine oil) and should be changed as recommended by your car’s manufacturer. If the PCV valve is not changed as advised, excessive oil will blow through the PCV valve and enter the air intake system.
What’s the solution? If it is confirmed that a clogged PCV valve is the source of engine oil inside your air filter or air intake system, is should be changed, the air intake should be cleaned, and a new air filter should be mounted.
- Worn Piston Rings
A second potential source of engine oil leaking into the air filter housing is because of a worn piston ring. The piston rings are mounted on the outer edge of the pistons inside the combustion chamber. The rings are meant to produce a combustion ratio and allow small amounts of engine oil to continue lubricating the inner combustion chamber during each piston stroke. When rings wear out, they loosen and could cause oil ‘blow-by’ — often displayed by blue smoke coming from the vehicle’s tailpipe while driving. In the early stages of worn piston rings, excessive oil blow-by could cause excessive pressure to build inside the crankcase, which sends more oil through the PCV valve and eventually into the air intake, as noted above.
What is the solution? If you observe engine oil in the air filter or intake housing, a professional mechanic might recommend a compression test. This is where a mechanic will mount a compression gauge on each individual spark plug hole to inspect the compression of each cylinder. If the compression is below what it should be, worn piston rings are often the culprit. Unfortunately, this repair is not as easy as changing a PCV valve. If worn piston rings are confirmed as the source, it might be a good idea to start searching for a replacement vehicle, as changing pistons and rings will likely cost more than the value of the car.
- Clogged Oil Passages
The last possible reason engine oil will find its way into the air intake system and eventually clog the air filter is because of clogged oil passages. This symptom usually happens when the engine oil and filter have not been changed 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 produced and cause extra oil to push through the PCV valve and into the air intake.
What’s the solution? In this case, sometimes replacing the engine oil, filter, PCV valve, and changing the dirty air filter is good enough. However, if clogged oil galleys are found, it is usually recommended to flush the engine oil and change the oil filter at least twice within the first 1,000 miles to ensure the engine’s oil galleys are clear of debris.
What is the Work of the Air Filter?
The air filter on most modern combustion engines is found inside an air intake housing, which is mounted on the top of the engine. It is attached to the fuel injection system (or a turbocharger) and made to efficiently transport air (oxygen) into the fuel system to be mixed with fuel before it enters the combustion chamber. The main duty of the air filter is to remove dirt particles, dust, debris, and other impurities before the air mixes with liquid gasoline (or diesel) to become a vapor. When the air filter gets clogged with debris, it can cause the engine’s fuel efficiency and power output to decrease. If oil is discovered inside the air filter, it can equally significantly impact the engine’s performance.
If you are finishing a routine service on your vehicle, truck or SUV, and discover engine oil inside your air filter or air intake housing, it’s likely a good idea to have a professional mechanic get to your location to complete an onsite inspection. Properly identifying the root source may save you a tremendous amount of money in big repairs or even changing your car before it’s time.