When you take your car in for regular maintenance, there’s a good chance the mechanic will inspect your engine air filter to see if it’s dirty. Replacing air filters is one of the more profitable jobs shops can do because it typically takes only a few minutes to complete.
Knowing that, consumers can save money by paying attention when they visit a service center. Air filters are widely available at auto parts stores, and replacing one is a simple job most car owners could do by themselves in less than 15 minutes.
Here’s what you need to know about engine air filters:
As the name implies, an engine air filter filters air entering an engine, catching dust particles, sand, dirt, and other debris that could damage engine parts. Air filters are mounted in a fresh-air intake typically found at the front of an engine.
Air pulled into the car gets mixed with fuel in the combustion chambers, so it needs to be clean; if dirt or other debris gets inside the engine and into the engine oil, it could damage cylinder walls, piston rings, and other parts. That damage could lead to hefty repair bills.
Filters come in different sizes and shapes specific to certain vehicles, so one size doesn’t fit all. They can be made of pleated paper, cotton, or synthetic materials. Most are rectangular, but some are cylindrical or round, and they’re generally built into a plastic or rubber frame. When it’s time for a new one, the filter, and frame are replaced as a unit.
Two views of car air filters, with the new filter on the left and the old one on the right. / Photo credit: P_Wei, Getty ImagesMechanics warn that a dirty air filter will hurt a car’s fuel economy. Still, a 2009 U.S. Department of Energy study found that the electronic engine controls on modern vehicles are “sophisticated enough to keep a clogged air filter from affecting the vehicle fuel economy.”
The DOE tested three vehicles, a Buick Lucerne, Dodge Charger, and Toyota Camry, and compared their fuel economy and acceleration with a clean, new engine filter to the same attributes with a clogged filter.
The test simulated clogging by covering the air filters with shop towels, severely restricting airflow, and the DOE concluded the reduced flow had “no significant effect on fuel economy,” using federal fuel-economy test procedures. The measured drop in highway fuel economy ranged from none in the Camry to 1.4% in the Charger and 1.7% in the Lucerne.
A clogged filter did, however, slow each car’s acceleration. In acceleration runs from 20 mph up to 80 mph, the Charger was 6% slower with a clogged filter than a clean one, the Camry was 7% slower, and the Lucerne was 12% slower.
In today’s fuel-injected engines, electronic controls decide how much fuel to feed into the engine, based in part on how much air is going in. If a clogged filter reduces the amount of air coming in, those controls reduce the amount of fuel accordingly to maintain the proper mix for drivability, emissions, and other factors.
Engines, though, depend on good, clean air flow to produce power and brisk acceleration, so restricting the amount of air will impact performance.
Replacement frequency varies by automaker and driving conditions. Some manufacturers say the filter should be replaced every 15,000 miles. Others say every two years, while others say every 30,000 miles or longer. The recommended interval for your vehicle will be detailed in the maintenance schedule section of your owner’s manual.
Whatever your maintenance interval, it probably carries a caveat that the filter should be changed more frequently if you do most of your driving in dusty or dirty environments. That includes frequent driving on unpaved roads or in desert areas, but it can also apply to large urban areas with heavy traffic, a lot of diesel trucks, and industrial pollution.
A good rule of thumb is to inspect the air filter (or have a mechanic do it for you) at least once a year. If the filter is covered with dirt or full of insects, leaves, or other debris, it’s time for a new one. If there’s only a little dirt on the surface or only in one area, it’s probably good to go longer. Try brushing off the surface dirt and turning the filter 180 degrees to expose the clean area to the primary airflow.
If fanning the pleats of your air filter with your hand sends dirt flying and leaves your hand grimy, the filter should be replaced. Hold the filter up to a light and look at it from different angles to see how dirty it is below the surface.
Your air filter should be easy to access. / Photo credit: plherrera, Getty ImagesAir filters usually live in a rectangular housing at the front of the engine that will be easy to find and reach. Your owner’s manual should show the location of yours and how to open its housing to remove the filter. On most vehicles, clips will hold the housing cover in place, though some require a screwdriver to remove it.
When replacing the air filter, the new one doesn’t have to be from your vehicle’s manufacturer or the same aftermarket brand that was there before, but it does have to be the same size. If an air filter is too small, air will flow around it, and dirt can enter the engine.
At a parts store, an aftermarket filter designed to replace an original-equipment filter will generally run from $15 to $40, with some vehicles’ being more expensive than others.
Repair shops, on the other hand, will mark up the cost of a filter and likely charge you for installation. How much they’ll charge depends on the shop, but a filter that costs $30 at a parts store might be $50 or more when installed by a repair shop — after all, service centers have to be able to pay their mechanics and keep the lights on.
Vehicles also have a filter for the air that goes into their heating, ventilation, and air-conditioning systems, but it’s unrelated to the engine air filter.
The cabin air filter is usually located under the dashboard and behind the glove box, and the air that passes through it comes in at the base of the windshield and bypasses the engine. Cabin air filters often get dirtier faster than engine air filters and must be replaced more often.
A performance air filter may eek a few more horsepower out of your engine. / Photo credit:Several aftermarket air filters promise to boost horsepower and acceleration by creating better airflow. Some of these can be washed and reused, while others are bathed in an oil that’s supposed to extend their life — but you’ll pay for them.
A conventional aftermarket air filter for a Toyota Highlander, for example, costs about $17-$30 at a parts store, but a “performance” filter runs from $50-$66.
Do they work? Yes, because an engine that breathes better will perform better, but it won’t transform a slug into a sprinter. An independent test of a Subaru Crosstrek, for example, found that a performance filter added 4 horsepower (a little more than 2%) compared with an original equipment filter and improved its 20-60 mph acceleration by 0.2 seconds — gains that probably wouldn’t be perceptible in everyday driving.
Be aware, too, that high-performance filters might have a difficult-to-detect downside: Increasing air flow might trap less dust and dirt, and that grit could damage internal engine parts.
If you have questions about this story, please contact us at Editors@carfax.com
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Article QuickTakes:
Air filters are designed to trap contaminants like airborne particles, dirt, dust, and even noxious fumes. These inexpensive parts play a vital role in keeping the air going into your engine, and cabin, clean and free of the sort of junk you encounter driving.
Your vehicle has two common air filters: the cabin air filter and the engine air filter. Both need to be changed regularly to keep your car running in tip-top shape. Here’s what you need to know about the difference between a cabin air filter and an engine air filter.
Cabin air filters are designed to clean the air coming into your car's cabin and protect you and your passengers from everything from dust particles to mold spores, exhaust, and allergens. Typical cabin air filters are shaped like the filters used in home air conditioning units — they’re flat, with numerous surface pleats.
Regularly replacing your air filter can help keep your heating, ventilation, and air conditioning (HVAC) system running efficiently in both hot and cold weather.
Different manufacturers recommend different intervals for cabin air filter replacement, so it's important to consult your owner’s manual. In general, you should change your cabin air filter when you get an oil change. That’s every six to 12 months depending on how much you drive, where you drive, and your vehicle’s year, make, and model. Most dealerships can replace your cabin air filter for you, or you can pick up the right one at an auto parts store and do it yourself.
Cost varies depending on your vehicle’s year, make, and model. If you take your vehicle to your dealer for service, they will likely replace the air cabin filter with a manufacturer-approved version that can run from around $40 to upwards of $100. If you replace the filter yourself, it can be as affordable as $18 to $28.
Engine air filters usually come in three shapes: round, conical, and flat. An engine air filter cleans the air that enters your engine before combustion so that the air that helps the fuel ignite is cleaner and free of particulates potentially causing longer-term issues. Think of it as your car’s lungs. For every gallon of fuel injected, roughly 10,400 gallons of air flows through the filter. An average 25-mpg air filter will clean about 6.2 million gallons of air over 15,000 miles.
Most manufacturers recommend a new engine air filter every 12,000 to 15,000 miles, or about every three oil changes, but your owner’s manual will specify exactly. Your vehicle's year, make, and model will determine what type you need.
Most dealerships and mechanics will offer to change it for you, but you can save some cash by buying the right filter at an auto parts store and changing it yourself. Most engine filters are located under the hood toward the front of the vehicle, but consult your owner’s manual for the exact location and method for replacement.
Most engine air filters will cost between $20 to $85, depending on the year, make, and model of your vehicle, and whether you do it yourself or take your vehicle to the dealer or a mechanic.