Why Is There Oil In The Air Filter? (Causes & Solutions)

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oil in the air filter

Many of us know that we should regularly change our car’s engine oil to keep it running smoothly. However, many of us don’t realize that other vital components also require attention and that regular oil change isn’t always enough.

Believe it or not, oil can find its way into the air filter, and when it does, it will cause all kinds of problems. The air filter is meant to collect dust, dirt, and various impurities from the air — but not engine oil.

Sometimes, whenever your local service center changes your air filter, they will notify you that your oil has found its way within your air filter box or blended within your old filter. Although oil seeping into your air filter isn’t always indicative of devastating engine damage, it shouldn’t be ignored.

In this article, we’ll take a closer look at what happens when engine oil gets into the air filter and how to fix the issue. Stay tuned!

Reasons Why There Is Oil In The Air Filter

Oil in the air filter or pool of oil inside the air filter box appears to be an odd incident, given that it is the last something you might think to discover.

Oil in the air filter or casing is referred to as engine blow-by. It may be triggered by numerous factors that need to be addressed ASAP since it might end in or contribute to catastrophic engine damage. Also, excessive blow-by results in reduced fuel economy, horsepower, and engine performance.

Identifying the source of the lost oil may be time-consuming and will need at least one specialized instrument, which is usually offered for rent at any local parts shop. Below are the most common causes that cause your oil to reach the air filter.

Clogged Positive Crankcase Ventilation (PCV) System

In numerous circumstances, oil in the air filter box or air intake has anything to do with its PCV valve or positive crankcase ventilation system, either indirectly or directly.

The positive crankcase ventilation releases crankcase vapors such as blow-by gases that escape via the piston rings—to avoid moisture build-up and excessive pressure in the engine crankcase.

The positive crankcase ventilation (PCV) systems do this by regulating airflow thru the crankcase through a valve, though others employ a calibrated orifice instead.

Whenever the PCV valve is opened, new air is drawn into the crankcase via a breather line connected to your air intake.

This new air is subsequently drawn into your crankcase, resulting in a scavenging action that sucks blow-by gasses down the PCV valve and through your air intake manifold. The vapors are then pulled into the engine and consumed as part of the usual combustion cycle.

If your PCV system gets clogged, oily engine blow-by fumes start to accumulate and ultimately find their way back towards your air intake housing or air filter box. The calibrated orifice or PCV valve is often the source of the issue.


The PCV valve must be replaced periodically like an engine oil filter and air filter. Whenever your PCV valve becomes clogged and your technician determines that it is blocked due to the accumulation of oil within the vehicle filter, immediately replace your PCV valve. Clean your air intake system and replace the air filter as well.

Worn Piston Rings

Another typical route for engine oil to reach your air filter housing is via worn piston rings. Piston rings are primarily accountable for managing engine oil consumption and overall pressure where it circulates inside your engine.

Piston rings are placed surrounding the circumference of your pistons to assist in sealing the combustion chamber and preventing gases from escaping into the engine’s crankcase.

Regardless, they enable a small quantity of engine oil to get through to lubricate and condition the critical internals of the combustion chamber. If these piston rings fail, the compression force dramatically decreases, allowing for the leaking of extra engine oil than is necessary.

Engine oil leakage caused by worn piston rings is frequently followed by reduced acceleration and a noticeable white smoke emanating from the exhaust pipe.


Whenever you check your air filter and see engine oil within, you may be advised by an automotive specialist to do a compression test.

It is accomplished by inserting a compression meter into the apertures of each spark plug to check the compression of the cylinders. Once it’s determined to be lower than average, the cause is determined to be worn piston rings.

Any worn piston ring cannot be repaired. If you’re meticulous and choose to replace your pistons, remember that this will require disassembling and rebuilding your engine, which is a lengthy operation.

When this procedure begins, the best course of action is to search for another engine. This is because replacing a piston will run you much more than purchasing a new engine.

However, you can always opt to simply replace the old piston rings if it’s determined that your engine could still properly operate if provided with a new set of rings.

Clogged Oil Passages

Assess the regular maintenance plan for your car. Outrageously old and degraded engine oil accumulates inside the engine oil passageways over time, which could accumulate and cause more significant difficulties.

When the oil passageways are clogged by oil and engine sludge, it gets more complicated for the oil to flow from the top of your engine into its crankcase, causing oil to accumulate and pool within the cylinder head valve cover.

Heavily blocked passageways create pressure, which allows oil to flow past the PCV valve and through the air intake system tubes, where it drains through both air filter housing and filter. 


Acquire an engine flush solution and execute the instructions. Generally, you’ll pour the solution into your engine oil and let it run for a length of time.

After flushing your engine, extract the oil and replace it with new engine oil. Replacing the car air filter will reveal if the issue remains.

In certain circumstances, flushing the engine many times may be necessary to clean all oil passageways and resolve the problem thoroughly.

Aftermarket Air Filters

Air filters are responsible for removing debris, dust, pollutants, and grime that might impede lubricant flow and impair engine efficiency. Since the air filter operates in a pretty busy portion of an engine, it might sustain significant wear and tear over time.

Certain air filters are reusable, while others are not. If you persist in utilizing disposable or dirty air filters instead of replacing them, you might detect oil in the filter. Whenever you find oil in the air filter, too much oil might be the issue.

Engine Blow-by And Its Cause

While your engine is running, its crankcase naturally builds up pressure due to fuel, air, and oil seeping through its piston rings. This is referred to as blow-by. A slight blow-by is quite typical since the piston rings are incapable of totally sealing against engine cylinder walls. Extreme blow-by, on the other hand, might produce complications.

Increased blow-by decreases the engine’s fuel efficiency and horsepower since a portion of every combustion cycle is spent blowing the mixture towards air intake and crankcase. Also, blow-by burns faster than pure fuel and might be challenging to detect using sensors, affecting the air/fuel mixture and decreasing your fuel’s octane level.

This might result in pre-detonation or engine knocking. Whenever knock happens often or while the engine is under a heavy load, it might cause engine damage. When your engine seems to have an abnormal amount of blow-by, there are a couple of possible explanations; one of them is the oil in the air filter.


Suppose you’re still unsure what caused the oil to penetrate your air filter. Replace your engine oil and PCV valve if necessary. These are very straightforward maintenance tasks that may be accomplished simply at home.

It might be a more significant issue whenever the trouble continues, such as the worn piston rings. Although these piston rings are straightforward components, replacing the piston ring demands extensive engine dismantling.


What causes the oil in the intake manifold?

Whenever oil can’t flow properly through the oil passages, it accumulates at the cylinder head valve cover. Once the oil passage is completely clogged, the oil would penetrate your air intake manifold via the PCV valve.

Do you need to oil the engine air filter?

Oil is usually utilized in any performance air filter to catch dust, dirt, and other air contaminants that might otherwise reach your vehicle’s engine. However, you should only apply a clean and thin oil by rolling your air filter. Without re-oiling, airborne contaminants may readily penetrate your engine and inflict damage.

Is your oil filter the same as the engine air filter?

By comparison, the oil filter captures dirt that tries to enter the crankcase. On the other hand, the air filter traps dust, debris, and other particles, to provide clean air to the engine to ensure a better air/fuel mixture that helps good engine performance.

Is oil in the air filter box normal?

You begin to panic and wonder if there is a significant problem with your automobile. The sad fact is that oil in your air intake or air filter box nearly invariably implies a vehicle problem. Occasionally, the repair is affordable and straightforward.

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