Informational Guide

Oil In Air Filter?

Why is there oil in my air filter? If you see oil in the air filter during a tune-up, you know something is wrong that needs to be repaired. In this guide, we help get you back on the road by showing you what causes oil in the air filter and how to fix oil in an air filter. 

Engine Blow-By 

Why is there oil in my air filter box? As the engine runs, there's pressure build-up in the crankcase. As oil slips past the piston rings, it's called blow-by. At times, seeing a small amount of blow-by could be considered normal. However, you should always take note if you see an excessive amount.  

Blow-by can create a reduced fuel economy, and it can hinder the engine's performance. It also creates issues for the sensors to monitor a proper air-fuel balance. Blow-by can also lead to pre-detonation, otherwise referred to as a knock. If the engine continues knocking, engine damage can occur.  

Blow-by leading to oil in the air filter can be caused by several reasons. To determine how to fix it, you will need to look at the following causes.  

Clogged Positive Crankcase Ventilation (PCV) Valve 

Older vehicles vented blow-by directly into the atmosphere, yet it wasn't good for the environment to have this level of emissions. That's why the positive crankcase ventilation valve got created. It redirects blow-by into the air intake and reuses it. 

There will be times when the PCV valve requires replacement. If you avoid this maintenance and the valve gets clogged, the blow-by gets past the gaskets and seals onto the air filter. A stuck valve can also allow more oil into the intake.  

If you want to prevent engine oil in the air filter, you should follow the manufacturer's recommendation and replace the PCV valve. Most recommend it get replaced every 20,000 to 50,000 miles.  

Worn Piston Rings 

If there is oil in the air filter housing, the problem could be with the piston rings. These rings provide the seal found between the piston and the cylinder wall. It's needed to keep the force strong, ensuring the maximum amount of power from the engine.  

However, the piston rings can wear out over time. Sometimes, it's just because of the high mileage, but it can also be caused by poor maintenance. You might see horsepower numbers drop as the piston rings wear out. You will also notice more blow-by. The bigger the problem is, the more engine oil in the air filter housing there will be. 

To check the piston rings, a compression test must be performed with each cylinder. The pressure should be equal across the board. You can find this specification in your car's service manual. Sadly, the only way to repair a worn piston ring is to rebuild the engine, which can become expensive.  

Clogged Oil Passages 

If there is oil in the air filter of a car, the passages might be clogged. This is also why there's oil in an air filter with a diesel engine. If the oil is neglected and not changed, it will become thick to the point that it becomes sludge. Engine sludge is going to clog the channels that need to be free. With a blockage, the engine isn't getting the lubrication it needs, but there's also going to be blow-by as a result. 

Plus, oil starts to accumulate inside the intake, where it doesn't belong. This problem is going to reduce fuel economy, hinder horsepower and lead to engine failure. Regular oil changes are the most important way to prevent this from happening. However, once sludge accumulates, it's difficult to clean it all out. Plus, if the engine fails, you will be forced to rebuild it.  

Aftermarket Air Filter 

Why do I have oil in my air filter? If you can't pinpoint any of the other problems, you might want to consider the air filter you are using. If it is an aftermarket air filter, it might be reusable. Reusable filters need to have an oily film applied before they are used.  

If there's oil inside the filter, it could just be that too much was used the last time. If you apply too much, you want to clean it up and get it ready for reinstallation. Then, follow the manufacturer's recommendations to ensure a proper installation.  

oil in air filter

What Can Happen If There Is Oil In Air Filter? 

"Oh no, I found oil in my air filter." If this sounds like you, it's time to think about the consequences. Once 4 stroke engine oil is in the air filter, you have to make some quick decisions.

First, you must figure out what's causing the excessive blow-by. Is it just a little bit of oil, or is it accumulating?  

If the air filter becomes clogged up with debris, it will reduce the power and fuel efficiency of the car. Therefore, it should never be left unchecked.

cons of oil in air filter

 First, you want to fix the problem that's causing the blow-by, and then you need to install a new, clean filter. If you avoid fixing the problem, you might end up with an engine rebuild on your hands, which gets very expensive.  

How To Clean Oil Out Of Air Filter (Step By Step Guide) 

Why is there oil in my air filter box? Once you fix what's causing the oil, it's time to clean the air filter. Most of the time, you can do this with some simple household items. Here are some tools to gather: 

  • Bucket of clean water 
  • Microfiber cloth 
  • Vacuum 
  • Screwdriver 
  • Dish soap 

Here are the steps to follow, whether you want to clean the oil in an air filter on ATV models or there is Generac oil in the air filter. 

  1. 1
    Locate the air filter. Look in the owner's manual to find it. 
  2. 2
    Remove the air filter carefully. 
  3. 3
    Vacuum the air filter first to get rid of any dust, debris, and loose contaminants. 
  4. 4
    Wash the filter in a bucket with the dish soap. If you are using an air filter with a layer of oil on the housing, you might need to use specialized products. 
  5. 5
    Tap off the excess water from the filter. 
  6. 6
    Allow the filter to dry completely. 
  7. 7
    Reinstall the filter.  

You should check the filter again after a little driving to ensure there is no more oil on it.  

Why Is There Oil In My Lawn Mower Air Filter? (How To Fix) 

Why is there oil in my lawn mower air filter? There are several reasons there would be oil in an air filter on small engines. Whether you are dealing with Honda GX25 oil in an air filter, Honda GCV160 oil in an air filter or Briggs and Stratton 550EX oil in an air filter, you must start by figuring out what's causing it.  

Once you fix the problem, your best bet is to replace the air filter. While you can clean some air filters, for the price, it might be better to simply reinstall a new one. After a little more use, you should verify that there is no more oil in the air filter box. 

oil in lawn mower air filter

Common Oil In Air Filter Questions 

Does oiled air filter damage the engine? 

While the air filter itself isn't creating damage to the engine, it doesn't help the performance. Plus, the original problem causing the oil to accumulate will eventually cause permanent engine damage if not corrected.  

Should you replace the air filter if there's oil on it? 

Air filters are relatively inexpensive. For the cost, you might as well replace it. However, some varieties can also be cleaned if you want to save a buck or two.  


Why is oil in my air filter? Whether you are dealing with 5.7 Hemi oil in an air filter or oil in an air filter turbo diesel engine, you must resolve the problem before it leads to damage to the motor. Take it as a warning sign that something is wrong.