An air filter is designed to clean air that is coming into a system from an outside source. You’ll find them in all sorts of applications, including HVAC systems in homes and buildings. The ones in your car work in a very similar way.
Changing your air filter is one of the most crucial parts of routine maintenance, but it’s also one of the simplest car tasks there is. Learning about the different types and materials will help you pick the best one for your vehicle.
Types of Car Air Filters
There are two main types of air filters in a modern car: Engine air filters and cabin air filters.
What Is an Engine Air Filter?
The engine air filter provides clean air to the engine by filtering it before it goes into the air intake. Engine air filters have been around for about as long as cars themselves. Engineers quickly realized the damage that could occur if large particles were allowed to be ingested into the motor.
There are a variety of shapes and materials available, which we’ll discuss below. Most filters use a corrugated design that increases the total surface area for blocking debris.
Where Is an Engine Air Filter Located?
The location of the engine air filter is different for every vehicle, and you should check your owner’s manual to be sure. However, they’re often in the front right or left corner of the engine bay near the headlights.
You can follow the air intake tube back from the engine itself to find the filter’s location. It’s usually in the sealed airbox. The airbox lid can sometimes be popped right off. For other models, you’ll need to unscrew the bolts holding it in place.
If you have a carbureted engine or short ram/aftermarket intake system, it should be easier to find since it'll be a large cone or ring.
How Often Should You Change Your Engine Air Filter?
Most engine air filters need to be changed or cleaned every 15,000 miles. You should follow the recommendations in your owner’s manual for air filter changes.
How to Tell If Your Engine Air Filter Is Dirty
A dirty air filter is easy to spot. If there’s loose dirt packed between the folds or it’s dark gray or black in color, it definitely needs to be replaced. If you hold a paper filter up to a light source and can’t see light coming through, you might need to swap it out.
Sometimes, a slight drop in performance or efficiency might signal that your air filter is dirty. However, a dirty air filter isn’t likely to have a noticeable impact on performance. But it never hurts to give it a quick glance every 5,000 miles or sooner.
What Is a Cabin Air Filter?
A cabin air filter provides clean air to the passengers by filtering it before it’s distributed by the climate control system. It prevents dirt, dust particles, and allergens from contaminating the air inside the vehicle.
Cabin air filters became widespread in the early 2000s. Many vehicles made before then won’t have a cabin air filter.
Where Is a Cabin Air Filter Located?
The cabin air filter is typically located in the interior, usually inside or below the glovebox. You can replace these yourself, but it can be harder to access than the engine air filter.
How Often Should You Change Your Cabin Air Filter?
The cabin air filter should be changed every 20,000 miles or so. Check the owner’s manual for your service interval. A cabin air filter replacement is often performed by dealers or mechanic shops, but you can also do it yourself.
How to Tell If Your Cabin Air Filter Is Dirty
A bad smell (musty or moldy) or stale air coming from the AC system can be a symptom of a bad cabin air filter. It’s definitely worth checking your filter when this is the case. If you find it to be gray and dirty, it’s worth spending the money to change it. They’re usually pretty cheap.
Car Air Filter Materials
There are three main types of materials used for engine air filters: Paper, synthetic, and foam. Cabin air filters are almost always paper, but some are made of synthetic materials that can be cleaned and reused. Foam air filters are very rare in cars, but sometimes used in particularly harsh environments.
Paper Air Filters
Paper engine air filters are the most common kind. Virtually all cars come with paper air filters from the factory. Most drivers will replace their air filter with a paper one as well.
Paper Engine Air Filters Pros and Cons
Car manufacturers want the engine to receive the cleanest air possible. As a result, paper filters tend to be very dense and good at filtering out small particles. However, this high air quality often comes at the expense of less airflow. This is the main reason enthusiast drivers swap their stock filters out for performance-oriented ones.
You can’t clean a paper air filter like you can a reusable synthetic one. You simply replace them every 15,000-20,000 miles. If you drive in dusty or dirty environments, shorter intervals are recommended. While paper filters are cheaper upfront, a reusable filter can save you money in the long run.
Reusable Performance Air Filters
Reusable air filters are typically made of synthetic gauze or cotton. Often, a wire mesh layer is put on the outside for added structure and filtering capabilities. These filters are designed to maximize airflow, giving your engine a bit more air to burn.
Reusable Engine Air Filters Pros and Cons
|Better performance potential
||Has to be cleaned
Performance air filters can give you better power and throttle response. In truth, we’re talking about very minimal gains. You won’t really see noticeable air intake benefits unless you get a complete cold air intake and an electronic tune to go with it. A much more noticeable benefit is the increased sound of air being drawn into the intake. This is especially true for engines with forced induction, like a turbocharger.
Even if you don’t care about extra performance, the ability to wash the filter and reuse it is a big reason to upgrade. As long as you clean and maintain them, they can last for up to 100,000 miles or more.
On the downside, you might have marginally worse air quality due to the increased amount of air that’s allowed in. But this is debatable and isn’t significant enough to worry most drivers.
Though you can save money in the long run, reusable filters have a higher upfront cost. Some owners don’t want to bother with cleaning their filters. Plus, many reusable air filters require oil for proper operation.
Some of the top brands of performance air filters include K&N, AirRaid, Injen, and JLT.
Foam Air Filters
Foam engine air filters are the rarest kind for cars. They’re often used in machines that run in very dirty environments, like ATVs, tractors, dirt bikes, and cars in extreme motorsports like rally racing.
For cars, foam is more commonly used as a protective wrap over a cone filter. Foam wraps, like this K&N one, can improve your filter’s effectiveness in extremely dusty environments.
Foam Engine Air Filters Pros and Cons
|Good at filtering dust
||Difficult to clean and oil
While paper and synthetic filters will draw in less air when debris is stuck on their surfaces, foam filters don't suffer from this problem as much. That's because foam filters have more air passages than surface filters do. This enables them to work well even when conditions are very dusty.
On the downside, foam filters are tough to properly clean and oil (which is required for effective use). They'll also break down over time if they're not properly maintained. Small bits of the broken-down filter can then be ingested into the engine, potentially causing damage. It’s for these reasons that foam is usually used in conjunction with other filters, rather than as the sole air filter.
Engine Air Filter Shapes
Engine air filters come in a variety of shapes. The configuration depends on many factors including the type of intake system the vehicle has and whether it’s factory or aftermarket.
Rectangular Air Filters
A rectangular (or panel) engine air filter comes standard on most vehicles. However, some performance air filters are also rectangular. They fit squarely into the airbox, which is the protective case around the filter. The airbox helps prevent excess hot air from entering the engine. Rectangular filters work just as well as any other shaped filter but don’t provide the same style to the engine bay as an uncovered cone-shaped filter.
Cone Air Filters
Many performance engine air filters are cone-shaped or cylindrical. Most are aftermarket, but some performance cars come with conical air filters from the factory. You can swap your stock rectangular filter out for a conical one with ease. They’ll fit nicely in the airbox with no issues if they’re approved for your car model.
A cone-shaped filter has increased surface area for air to be drawn in. Most aftermarket cold air intakes include cone filters. However, a filter on its own will only add minimal power gains.
Check out some examples below of universal air filters in this layout.
Circular Air Filters
Many older engines, specifically carbureted ones, use a circular or oval-shaped engine air filter. Since the carburetor (where air and fuel mix) is on top of the engine, these donut-shaped air filters sit on top of the motor.
This provides an opportunity to show off a good looking design when you have your hood popped at a car show. For that reason, many classic car enthusiasts care a lot about which air filter and air cleaner they choose.
Does It Matter Which Air Filter You Use for Your Car?
For most drivers, it doesn’t matter which type of air filter they use. Performance drivers that are adding other mods will often switch to a performance air filter right away. It’s a very affordable component that literally takes a couple of minutes to install.
Even if you’re still rocking the stock air filter, you’re hardly missing out on “hidden horsepower” from your engine. You might only get a few more horsepower from a performance air filter. But a cold air intake and electronic tune can offer a 10 hp or more increase. Many cold air intake kits include a performance air filter.
At the end of the day, the best air filters for your car are the ones that are clean.