Oil in the Air Filter – What You Should Know

Ever conducted some routine check on your air filter? You are sure to notice some contaminants, debris, and dirt. Nevertheless, a healthy air filter shouldn’t contain oil. But, what happens when there is oil in the air filter? That can be catastrophic and often results from “blow-by,” a situation where the combustion gases leave its chamber and go into the crankcase.

The engine often requires engine oil for proper functioning, but it shouldn’t be in the air filter. Once noticed, that could be a sign that your engine could be facing some serious issues. It would be best if you quickly savage the situation before anything goes wrong.

What Causes Oil in the Air Filter?

As you try to figure out the detriments of oil sitting in the air filter, it is crucial to know what causes the air filter’s oil filter. Indeed, engine oil does a fantastic job preventing excessive friction between the machine’s heating parts as they move.

oil in air filter atv

Also, the oil can help reduce overheating cases, as it allows the refrigerant or coolant to travel across the entire engine. Before I talk more about the reasons you find oil in the air filter, you must understand the air filter’s work.

It works effectively in ensuring the engine “breathes” with ease. Hence, you can rest assured that the engine would perform efficiently. It traps the built-up contaminant and debris that stands as potential threats to the engine. Then, during your routine checks, you clean the air cleaner and remove the accumulated dirt.

There’s oil in my air intake; what should I do? What causes the oil in the air filter of a motorcycle engine? Should I feel concerned with oil coming out of the air filter diesel engine? These and more similar questions keep lingering in most folks’ minds as they care for their engines. Nevertheless, the main reason why you have oil in your engine’s air filter is due to a condition known as “Blow-by.”

Your engine can run smoothly thanks to the pressure built-up in the crankcase from the oil, air, and fuel that sips through the piston rings. Still, it is recommendable that you keep a close watch on your engine’s lean or rich running to avoid sudden damage. When Blow-by occurs in a small amount, it seems pretty normal, and the piston rings do not seal against the “cylinder walls.”

 But, there is a huge problem when there is a case of excessive blow-by. In such a case, there is reduces horsepower and fuel economy that results from the wastage of some combustion cycle with the mixture venting into the air intake and crankcase. Such a situation can even result in engine knocking.

With that in mind, you should go through these common causes of oil getting into your engine’s air filter.

Clogged PCV (Positive Crankcase Ventilation) Valve

“Why is there oil in my generator air filter?” Well, it could be a case of a clogged PCV valve due to the presence of some contaminants. Kindly note that these PCV valves help control the emissions of harmful gases from engines. They help redirect blow-by into the air intake rather than causing some severe pollution of the environment.

There is a need to replace the PCV valve, just like changing the oil filter occasionally. Once the engine’s PCV valve becomes clogged, it may result in the blow-by sipping into the PCV seal that appears between gaskets or other tiny spaces. Again, you may start noticing the valve allowing more oil intake than intended.

Worn-out Piston Rings

The piston rings are those seals between the piston and the cylinder walls that help increase the force that the air-fuel mixture combustion applies in the combustion chamber. When the force appears firmer, you would find your engine having added strength. Kindly note that excessive oil consumption and increased exhaust smoke common symptoms of a “bad” piston ring.

Based on the engine part’s location, you can start noticing your piston rings succumbing to wear and tear. With extensive stress relating to wear and tear, the engine might have a damaged or broken piston rings. Do you find it challenging to tell if your piston ring is faulty? Well, you can check the cylinder’s pressure, ensuring it is the same as that of other cylinders.

Clogged Oil Path or Channel

There is no doubt that modern engine oils can last for a long time, but folks need to change them at intervals. When you forget to change the engine oil, you would find a nasty nudge forming in the engine. With that, the engine paths get blocked, and the sludge may get to other places where they shouldn’t be. So, a case of oil in the air filter of a diesel turbo engine or oil in an air filter ATV may result from clogged oil channels.

Aftermarket Air Filters

The excessive work that goes on in the air filter can subject it to extensive wear and tear after much use. Some air filters in the engine are reusable, whereas some are not. Kindly note that brands like K&N are reusable aftermarket air filters. With such reusable options, you have to follow the manufacturer’s recommendations to prep and clean the filter.

oil in air filter turbo diesel

When you decide to change the air filter, you may only need to apply some oily film on the outer part before use. Kindly note that a damaged or dirty air filter can reduce the engine’s airflow and create an air-fuel imbalance. Such a case can result in a bad spark plug and cause the “check engine” light to turn on.


What does it mean if there’s oil in the air filter?

When there’s oil in your air filter, it relays that the engine’s crankcase has the excessive deposition of carbon or a formation of engine sludge. Such a situation often results from the PCV valve appearing faulty due to the built-up debris.

Secondly, a worn piston ring that keeps gases sealed within the combustion chamber can cause oil to get stuck in the air filter. Furthermore, a dirty or damaged air filter and a clogged oil channel can also cause the air filter’s oil filter. Nevertheless, you can salvage this situation with the right tools and ensure the engine works effectively.

How do I get oil out of my air filter?

If you find oil in the air filter of a lawnmower engine, it would help remove the air filter, doing so carefully. Then, ensure that you clean the air boot, remove any dirt you find there, and spray using some contact cleaner. Then, soak the engine’s air filter in a suitable cleaner to get the contaminants out.

Once done, removed the submerged air filter and squeezed the excess moisture out of the filter. It would be best if you wash and rinse afterward using a suitable automotive solvent. You should inspect the air filter for any possible holes during this process and any need for a replacement. Apply some oil to the filter once it gets dry and gets the filter cage cleaned before reinstalling it.

Does an oiled air filter damage engine?

A light coated oil in the air intake manifold seems fine, and there is no need to get worried over such. The tiny amount of oil present would ensure the filter does not pass more dirt. Still, it is crucial to maintain and clean the oiled filters; they may seem detrimental to the engine’s overall performance.

There are reported cases of oiled filters damaging the Mas Airflow Sensor of the engine. Once the air filter gets dirty or nasty, it is necessary to clean and replace it if the need arises. If there is any need to re-oil the filter, it would help if you stick to the manufacturer’s instructions.

Will a clogged ‘air filter’ result in excess oil consumption?

Yes. The excessive consumption of oil is a mechanical problem that often results from oil leakage. Nevertheless, it can be a case of leakages from the crankshaft seals and the gasket cover valve. There are greater chances of the engine consuming more oil when the air filter gets clogged with dirt and other contaminants.

The intake tract restriction that results from the clogged filter would get the vacuum levels increased. Hence, such activities weaken the oil seals. The higher vacuum pulls the oil past the seals and causes the engine to burn excessive oil.

How To Clean and Oil an Air Filter Motor Cycle (YouTube)

Final words

An engine’s air filter is crucial for its functionality, as it allows the engine to work efficiently. It helps trap various contaminants, including sand, dirt, and grime, that might harm your engine. But, what happens when there’s oil in the air filter? Well, such a situation can cause some significant damages to the engine if not savaged on time.

These often result from blow-by caused by a damaged PCV valve, work-out piston rings, and clogged oil channel. Hence, this article explains more about the causative factors behind oil getting into the air filters. A quick glimpse would give you a better understanding.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

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