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How to Clean, Oil, & Maintain Your Car’s Engine Air Filter

Your engine air filter prevents dirt, dust, and debris from entering your vehicle’s engine through the air intake system. When the air filter becomes dirty or clogged, your engine has to work harder to draw in the air it needs, leading to sluggish acceleration and reduced fuel efficiency. This guide explains the differences between oiled and conventional engine air filters, how to clean and re-oil a reusable filter, and how often each type should be cleaned or replaced.

Tools & Materials List

Step-by-Step Instructions

How Often Should You Service Your Engine Air Filter?

Frequently Asked Questions

Types of Engine Air Filters

Vehicle air intake systems use two types of air filters: one-time use conventional filters and reusable oiled filters. Conventional filters are made of paper or foam and get replaced once they’re dirty, while oiled filters use an oil-coated cotton element that can be cleaned and reused.
Conventional Engine Air Filters

Conventional Engine Air Filters

Conventional engine air filters, also known as “dry” filters, are used in most vehicles from the factory. Made from thick paper or foam, these filters block nearly all contaminants but restrict airflow more than oiled filters.

As dirt and debris build up, airflow becomes further restricted, which can reduce fuel efficiency and performance and, if left unaddressed, may eventually cause engine problems. Conventional filters are cost-effective and ideal for normal highway driving, but they aren’t reusable. Once clogged or damaged, they should be replaced.

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Oiled Engine Air Filters

Oiled Engine Air Filters

Oiled engine air filters, also known as performance air filters, use open-cell cotton filter elements coated in oil to trap dirt and debris while allowing more airflow than conventional filters. This increased airflow makes them popular in aftermarket drop-in filter upgrades and cold air intake kits for trucks, SUVs, and performance vehicles.

They’re also durable and provide great filtration in dusty or off-road conditions. Most oiled air filters, including K&N air filters, come pre-oiled and are installed like a standard filter, though some specialty and racing filters ship unoiled. Unlike conventional air filters, oiled filters are washable, reusable, and can last longer without a reduction in performance when properly maintained.

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Tools & Materials

Engine Air Filter Engine Air Filter
Air Filter Service Kit Air Filter Service Kit
Shop Towels Shop Towels
Safety Eye Glasses Safety Glasses
Protective Gloves Safety Gloves

How to Clean & Re-Oil an Engine Air Filter

Auto parts professional cleaning an engine air filter

Step 1: Clean the Engine Air Filter

Spray both sides of the engine air filter with filter cleaner, either top and bottom or inside and outside. Let the cleaner soak into the filter, but don't let it dry.

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Auto parts professional rinsing an engine air filter with water

Step 2: Rinse the Engine Air Filter

Once the cleaner has had the chance to soak in, rinse it out with cool, low-pressure water. Leftover cleaner often appears white, and if your filter has pleats, it could remain on those pleated edges. Once you've rinsed off all the cleaner, let the filter air-dry completely.

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Auto parts professional applying oil to an engine air filter

Step 3: Apply Fresh Oil to Engine Air Filter

Apply fresh filter oil to your fully dry air filter. You can buy filter oil in a squeeze bottle or aerosol form. Apply oil only to the side of the filter that air will flow into. If you’re using squeeze-bottle oil, apply a thin layer to the ridge of each pleat, or an even coat across the surface. If you're using aerosol oil, hold the nozzle about three inches from the filter and spray evenly across the top of each pleat, or over the surface.

Once you've applied the oil, inspect the filter to make sure it’s evenly distributed. Most filter oils are brightly colored so that you’ll be able to see any runs or uneven spots. Touch up the filter as needed to make sure the coverage is as even as possible.

Pro Tip: To protect your vehicle’s MAF sensor, don’t over-oil your filter. If you see any areas of excessive oil or drips, use a clean shop towel or rag to dab up the excess.

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Auto parts professional holding an oiled engine air filter

Step 4: Let the Oil Set & Reinstall the Engine Air Filter

Let the oil soak in for 15 to 20 minutes before reinstalling the air filter in its housing.

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How Often Should You Service Your Engine Air Filter?

Conventional engine air filters, commonly used for highway driving, should typically be replaced once a year or every 12,000 to 15,000 miles; whichever comes first. If your vehicle operates in dry, dusty conditions, consider replacing the filter every 3,000 to 6,000 miles, or as often as needed to prevent any performance issues.

Oiled engine air filters don’t need to be replaced as often, but they do require regular cleaning and re-oiling. Under normal highway driving, drop-in replacement oiled air filters can last up to 50,000 miles between services, though dusty or off-road conditions may shorten this interval. Most oiled performance air filters can be cleaned and re-oiled, while some specialty filters must be replaced once dirty.

For more information about servicing your oiled engine air filter, check the manufacturer’s recommendations on the packaging or visit your local O’Reilly Auto Parts store, and our parts professionals will be happy to help you.

Frequently Asked Questions: Engine Air Filters

Are oiled engine air filters bad for my engine?

Oiled air filters should not cause any issues with engine performance when they’re installed and maintained correctly. The main risk is over-oiling: excess oil can coat your vehicle's mass air flow (MAF) sensor, throwing off its readings and causing rough idle, hesitation, or a Check Engine light. Applying a thin, even coat and wiping off any excess oil can help prevent this, but if you notice MAF sensor or fuel trim codes after oiling your air filter, consider cleaning your MAF sensor.

How often should I clean a K&N engine air filter?

Under normal highway driving, K&N's drop-in replacement engine air filters last up to 50,000 miles between cleanings, while the larger conical filters used in cold air intake systems can go up to 100,000 miles. Dusty conditions or off-road driving can reduce that interval to as little as 25,000 to 30,000 miles, so be sure to check your filter regularly.

Can an oiled engine air filter improve gas mileage?

Oiled engine air filters don’t significantly improve gas mileage. Although they may boost airflow, modern computerized engines automatically adjust fuel delivery to match the increased air, making any improvements in fuel efficiency negligible or unnoticeable. However, oiled air filters can enhance engine performance. The increased airflow helps your engine breathe easier, supporting better throttle response and acceleration.

How much horsepower does an oiled engine air filter add?

An oiled engine air filter typically adds 1% to 4% more horsepower, which is often negligible in testing. The bigger performance improvements from cold air intake systems come from more than the air filter. They also include larger pipes and a bigger airbox, which work together to improve airflow and overall engine efficiency.

What happens if my engine air filter doesn't seal properly?

If the filter doesn't seat correctly in its housing, air can bypass it entirely through the gap and enter your engine unfiltered, which may allow dirt and debris into the engine and lead to damage or premature wear. Inspect the housing and seal for cracks or damage every time you remove the filter, and make sure it's fully seated before closing the housing.