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Have you noticed something in your car’s air filter that looks oily? Maybe you’ve bought a used vehicle and are facing engine problems. If you found engine oil in the air filter, it could point to a few possible issues.

The primary purpose of an air filter is to capture impurities and waste but not oil. At the same time, the oil moves around the engine to lubricate the moving parts. These two elements work independently and without any overlap. Therefore, finding engine oil in the air filter is generally not natural.

“Blow-by” is the most common cause of oil in the air filter. Let’s explore it in greater detail below.

What is Blow-By?


Blow-by happens when the air-fuel mixture or combustion gases flee from the combustion chamber into the crankcase (also known as the oil pan, where the engine oil is stored) at the bottom of the engine.

The crankcase ventilation system pulls these gasses from the crankcase and re-enters them in the air intake system using a special one-way valve. This ventilation system effectively removes combustion gases between the piston and liner.

Such a small blow-by is entirely normal. But underlying problems within the crankcase ventilation system can lead to a more extensive leak and cause the engine oil to slip past the air filter.

Now that you know how oil might get in your air filter, let’s discuss why this happens, its symptoms, the potential effects on your engine, and what you need to do.

Let’s Discuss the Top Three Reasons Engine Oil gets in the Air Filter

Faulty PCV (Positive Crankcase Ventilation) Valve

Old cars used to vent blow-by that was harmful to the environment. The establishment of the positive crankcase ventilation (PCV) valve was one of the first emissions control systems. It redirects blow-by back into the air intake instead of letting it pollute the environment.

But, the Positive Crank Ventilation (PCV) Valve is a widespread reason for clogging an oily air filter. Its role is to recirculate blow-by gases back into the air intake. The gases then transit back into the combustion chamber to get a second chance at ignition.

Pressurized blow-by gases force themselves through seals or other gaps when a PCV valve gets blocked. If the PCV valve opens, it can allow oil to penetrate and contaminate the air filter. You can avoid these issues by changing the PCV valve regularly when needed.

Mainly manufacturers state replacement intervals for this valve; if you don’t remember when you last replaced it, it’s been too long. The good news is this valve is relatively inexpensive.

What is the Solution to a Faulty PVC?

If your blocked PVC valve is the source of engine oil in the air filter, you should replace, clean, and install a new air filter. However, that may not be enough, mainly if worn-down piston rings cause the presence of engine oil in the filter.

Worn Piston Rings

Piston rings act as a seal between the piston and the cylinder wall. They maximize the force applied by the combustion of the air-fuel mixture in the combustion chamber—the tighter your piston rings, the more power your car will have.

However, with time, piston rings can become worn down due to improper maintenance, high mileage, poor engine design, or running the engine hard before it has reached operating temperature.

With the car’s increasing age, horsepower slowly declines. The blow-by gradually increases as the quality of this seal deteriorates. Whereas when the volume of the blow-by starts to rise, you may notice more engine oil in the air filter.

What’s the Solution to Worn Piston Rings?

A professional might recommend a compression test if you notice engine oil in the air filter. This is where a technician will install a compression gauge on the spark plug hole individually to check the compression of each cylinder.

If the reduction drops down than it should, worn piston rings are usually the culprit. Unfortunately, this repair is a little more complex than replacing a PCV valve. If worn piston rings are picked to be the source, it might be suitable to start looking for a replacement vehicle, as replacing pistons and rings will likely cost you more than the car’s value.

Clogged Oil Passage

Clogged Oil Passage

Oil filters can last long, but they won’t last indefinitely. Changing the oil and filter is essential. Old oil or a failed filter can wreck engines.

The oil leak in the air filter can also occur due to polluted engine oil. This is due to gasses failing to vent or lack of maintenance. When the engine oil gets saturated with dirt, it tends to stick, leaving residues along the oil passages as it lurches around.

Clogged oil passages also create excessive pressure around the channels, which causes the blow-by effect to pull more engine oil than necessary. The symptoms of a blocked oil passage are not very clear, and scanning for them might not be easy for everyone. Though if your oil passages are clogged, a mechanic will recommend a complete engine flush as a mere oil replacement will not solve it.

So What’s the Best Solution for When Engine Oil Gets in the Air Filter?

If you frequently find engine oil in your air filter, then changing the PCV valve, engine oil, and dirty air filter is mandatory. However, at the same time, replacing the oil filter and flushing the engine oil at least twice is also advisable. It is recommended to ensure the engine’s oil galleys are clear of debris within the first 1,000 miles.

If you complete routine service on your car and discover engine oil in the air filter, it’s probably a good idea to call a professional mechanic for an onsite inspection. Correctly identifying the root source of the problem may save you tremendous money in major repairs.

Engine Oil Keeps Getting in the Filter? Repair Or Sell? What’s the Better Option?

Engine Oil Gets in the Air Filter

Or you can skip getting all these repairs done altogether and swap your old, bothersome vehicle for a brand new one.

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