Have you ever gone to change your air filter and found things a bit oily? Perhaps, you have recently bought a used vehicle and are wondering if there is an issue hiding under the hood?
Finding engine oil in your air filter is not a bad thing but could be pointing towards a few potential issues. More than likely, the culprit is a blow-by.
What causes Engine Blow-by?
When the engine runs, there is a natural build-up of pressure in the crankcase from fuel, air, and oil slipping past the piston rings. This is popularly known as blow-by. A little blow-by is totally normal as the piston rings are not able to seal perfectly against the cylinder walls. However, too much blow-by can cause various other problems.
Excessive blow-by leads to decreased fuel economy and horsepower numbers, as some of each combustion cycle is wasted venting the mixture into crankcase and intake of air. In addition, blow-by burns that are different than pure gasoline and can be difficult for the sensors to measure, obstructing with the air-fuel ration and efficiently lowering the octane rating of gasoline.
This may result in pre-detonation. Knock can cause engine damage if it happens daily or if it occurs when there is too much load on the engine. If your vehicle seems to have too much blow-by, there are a few causes behind this.
Common causes behind oil in Air Filter
Jammed Positive Crankcase Ventilation Valve- Old cars used to vent blow-by to the atmosphere, but this kind of emissions caused harm to the environment. The positive crankcase ventilation valve was launched as one of the first emission control and redirects blow-by back to the air intake rather than allowing it to cause pollution in the environment. A Positive Crankcase Ventilation valve must be replaced occasionally, similarly like an oil filter. The positive pressure in crankcase must have a place to go. If the PCV valve gets blocked, blow-by may end up slipping through the seals, between the gaskets and any other small gaps in the engine which it can find.
Worn Piston Rings- Piston rings offer a seal between the cylinder wall and piston to increase the force which is applied by combustion of air and fuel mixture inside the combustion chamber. The stronger the force, your car will have more power. With time, piston rings can become worn because of high mileage, wrong maintenance, and poor design of the engine. As a car becomes old and piston rings wear, you might see the horsepower numbers slowly decreasing and blow-by slowly increasing as the quality of this seal diminishes. When the volume of the blow-by starts increasing, you may notice more oil in the air filter housing, extending all the way to the air filter.
Aftermarket Air Filter- Some of the aftermarket air filters like the popular K&N brand is recyclable. These filters need an oily film to be applied to the outer part of the filter before using. If you find oil on the inner part of the air filter, it may be because you or the previous owner might have too much oil. You must follow the filter manufacturing company’s recommendations on how to clean and prepare the filter before reusing.