Oil in Air Filter – Common Causes and Viable Solutions?

Oil in air filter is not dangerous; however, don’t take it for granted as it can prevent enough air from entering the engine for combustion. The air filter ensures that no contaminant enters the engine to compromise combustion.

Oil in Air Filter

In the process, it could get clogged by these contaminants, including oil, leading to a lean air/fuel mixture. This article will discuss why oil gets into the air filter and how to fix it.

What Causes Oil in the Air Filter?

The causes of oil in the air filter include a blocked positive crankcase ventilation valve, damaged piston rings, and blocked oil channels. Some after-market oil filters can also allow oil to sneak into the air filter; which is why we encourage you to do your checks before purchasing one.

  • A Blocked Positive Crankcase Ventilation Valve

A positive crankcase ventilation (PCV) valve allows exhaust gasses to leave the crankcase and is found at the bottom of the engine. The positive crankcase ventilation system filters air into the engine and recirculates the gasses to reduce emissions. The crankcase also stores engine oil which circulates throughout the engine. As the PCV valve filters the air, it’ll eventually get blocked and stuck open.


This “stuck open” position allows the oil to pass through the valve and enter the air intake system. Thus, the oil ends up in the air filter and damages it. You can do nothing to prevent the PCV from getting blocked, but changing it regularly will prevent the oil from getting into the air intake system.

  • Well-Worn Piston Ring Causing Oil Blow-by

The piston rings are located around the outer edges of the piston, and their main duty is to transfer heat from the piston to the engine’s cylinder wall. Additionally, they create a combustion ratio and also allow a small amount of oil into the chamber for lubrication.

Causes Oil in the Air Filter

The constant movement of the piston causes the rings to wear, which results in an oil blow-by. The oil blow-by is when the combustion gasses travel into the engine’s crankcase.

When the oil blow-by becomes excessive, it can cause more pressure in the crankcase, sending oil through the valve into the air intake. Thus, you’ll find oil in the air filter housing. The result is that you begin to see blue smoke coming from your vehicle’s exhaust pipe during driving.

  • Blocked Oil Channels Creating Engine Oil Pressure

Clogged oil passages can also cause oil to end up in the air intake and, eventually, the air filter. This happens when you refuse to replace the oil and filter as the car’s manual recommends.

The clog results from excessively dirty oil or sludge that forms due to excessive oil use in the crankcase. When the dirty oil doesn’t flow smoothly, it creates enormous amounts of oil pressure, which causes extra oil to flow through to the PCV valve into the air intake.

When excessive oil enters the air filter, the combustion chamber absorbs and burns it. The burning of the oil creates an exhaust gas which becomes difficult for the cat converter to convert into clean gas. Thus, the exhaust gas lines the surface of the catalytic converter and clogs it. If the issue isn’t addressed soon, the accumulation of that exhaust gas may destroy the converter.

  • Oiled Aftermarket Air Filter

Some brands of aftermarket air filters already come oiled from the outside. The reason is to prevent smaller particles from entering the air intake. Thus, don’t be surprised when you use these aftermarket products and see the oil on the air filter. It is just one of the ways to keep the air intake free from dust particles and other contaminants that might compromise the system.

However, some of the oil can get into the Mass Air Flow sensor if the aftermarket air filter is over-oiled during routine maintenance. Oil in the Mass Air Flow sensor can tamper with the airflow into the engine, leading to the wrong air-fuel mixture. A wrong air-fuel mixture will lead to performance issues such as loss of power.

The oil can also leak onto the spark plugs and cause engine misfires or engine idling, affecting engine performance. Oiled plugs result in the blue exhaust, which we discussed earlier, and excessive oil consumption.

How to Fix Oil in the Air Filter

Fixing oil in the air filter depends on the cause of the problem. If a clogged positive crankcase ventilation (PCV) valve is the cause, then you should replace it. However, if damaged piston rings are the problem, then we recommend you purchase a new vehicle.

The cost of buying and replacing worn piston rings could be equal to or higher than purchasing another vehicle. Solving the issue of blocked oil routes is simpler as it involves changing the oil, PCV valve, oil filter, and air filter. In some extreme cases, you’ll need to flush out the old oil and change the oil filter twice in the first 1,000 miles.

  • Replacing a Blocked Positive Crankcase Ventilation Valve

To undertake this job, you’ll require a ¼ inch driver, ¼ inch socket, pliers and a replacement valve hose. The first step involves locating the valve, which you can find anywhere on the valve cover, depending on the type of vehicle.

Fix Air Filter on Car

Next, remove the engine cover by unscrewing the bolts and nuts or removing the rubber insulators that hold it in place. Then remove the valve hose and the connectors.

Install the new valve hose according to how you removed it and clamp it to the valve using either the old or new connectors. Finally, replace the engine cover and all other car parts you removed earlier to access the valve.

  • Fixing Blocked Oil Channels

An engine oil change is one way to fix blocked oil channels. The tools you’ll need include a drain pan, funnel, jack stand, box end wrench, pair of gloves, oil and oil filter wrench. First, warm up your vehicle to ensure the smooth flow of the oil. However, don’t change your oil after driving a long distance because it will be too hot.

Next, lift and support your vehicle with the car jacks, then locate the drain plug under the car. Wear a pair of gloves and place the drain pan under the drain plug to catch the old oil. Next, unscrew the plug and drain the oil, ensuring that you have enough rags to clean any spillage. Wait till the oil drips slowly, and then examine the gasket at the base of the drain plug.

We recommend you change the gasket before screwing the drain plug in its place. The next task is to locate the oil filter and place the pan under it. Remove the old oil filter and fix a new one in its place, then replace the drain plug. Now, locate the oil fill cap, place a funnel at the top and pour oil into the engine, ensuring that you warm your car once again.

  • Solving Worn-out Piston Rings

If you try the above solution, but the problem persists, check the piston rings to see if they are the culprit. These checks can only be done by a professional mechanic as you don’t have the expertise and the tools to undertake such a complex task. The mechanic will conduct a compression test which involves installing a compression gauge in every spark plug’s hole.

The idea is to check the compression in every cylinder. When the compression in each cylinder is below the standard unit, the piston rings are the cause. Thus, they need replacement, which is a very complicated task. We’ll recommend you purchase a new vehicle, as discussed earlier, due to the high cost of replacing the piston rings.

  • Cleaning Air Filter With Oil in It

To clean the air filter with oil in it, ensure that the engine is cool to the touch to avoid burning your fingers. The next step is to remove the housing or any attachment to the air filter, ensuring that no debris falls into the air intake.

Now, spray the air filter with a cleaning solution until it’s all soaked, and allow it to sit for a few minutes. Then place the air filter under a faucet and open it to ensure it washes away the oil in the air filter.

Start washing the air filter from the interior and gradually make your way to the exterior. The idea is to prevent the oil from going further into the filter’s fibers. Dry the filter in an airy place to ensure it’s completely dry, and re-oil it. If your vehicle uses a mass airflow (MAF) sensor, re-oil with care, as over-oiling could compromise the MAF, as discussed earlier.

If the new filter is already oiled, apply fresh oil around the entire filter, including the lip and sealing flange. Place the new filter and attach the other components you removed earlier to it.

Frequently Asked Questions

– Is It Advisable to Clean and Reuse an Air Filter?

Yes, it is advisable to clean and reuse an air filter as long as the filter hasn’t been damaged by dirt. Some companies also produce reusable air filters that you can purchase. However, if the air filter is damaged, it’ll be difficult to reuse it.

– Can an Air Filter Be Cleaned With Water?

Yes, an air filter can be cleaned with water, but it might take longer to dry than using a dedicated cleaner. Place the filter under a running faucet and wash it from the inside out. Then dry the filter in a sunny and airy place to hasten the drying process.

– Can a Dirty Air Filter Affect Engine Performance?

Yes, a dirty air filter can affect engine performance by preventing the free flow of air into the combustion engine. Thus, the engine is unable to generate enough energy to power the vehicle and to keep running. This also causes the vehicle to lose power during acceleration.

Fixing Blocked Oil Channels

Can Using a Temporary Oil Cap Cause Oil to Get into the Air Filter?

Using a temporary oil cap solutions can potentially cause oil to seep into the air filter. It may not provide a tight seal, allowing oil to leak out and contaminate surrounding components. To avoid this issue, it is crucial to use a properly fitting and secure oil cap to maintain the integrity of your engine’s air filter system.

Can an Oil Light Issue Cause Oil to End Up in the Air Filter?

When dealing with a resetting vehicle oil light issue, it is important to consider its potential impact on the air filter. If the oil light remains illuminated for an extended period, it could indicate low oil pressure or a leak, increasing the chance of oil seeping into the air filter. Regularly checking and addressing any oil light issues promptly is crucial to prevent potential damage to the air filter and other vital components.


Oil in the air filter isn’t a dangerous sign, but excessive oil in the filter box can be detrimental to the health of the vehicle.

Here’s a recap of all that this article has discussed:

  • Excessive oil in air intake is a result of a blocked positive crankcase ventilation valve which allows the engine oil to pass through it to the air intake.
  • Damaged piston rings result in a blow-by, which causes excessive pressure in the crankcase, leading to oil leaking into the air intake.
  • Blocked oil channels create excessive oil pressure, which forces some oil down the air filter into the air intake.
  • You can replace the positive crankcase ventilation valve or the engine oil and filter to fix the problem.
  • However, we recommend that you purchase another vehicle instead of replacing the piston rings due to the high cost involved.

However, first, ensure your mechanic performs a compression test to determine if the problem is from the piston rings. You can also ask your mechanic to change the engine oil or replace the valve for you.

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