Why is the humble air filter so important to a car's engine? As you probably know, the three main contributors of a petrol engine's combustion cycle are air, fuel, and spark. For diesels, the spark is replaced by compression. For optimum combustion, all three should ideally be perfect. Yet while the fuel and electrical systems can be expensive to fix when something goes wrong, replacing an air filter is not only easy to do, but super affordable too.
An engine filter cleans the air going into the engine; cabin or pollen filters purify the air going into the cabin. Both are vital to machine and human inhalation alike. If you're allowing dirty, badly filtered air to enter your engine, it's not going to do it much good.
Air filter types
Engine air filters come in three different shapes: rectangular, conical, and circular. Rectangular air filters are the shape of filter you will find on almost every modern car. Even a Ferrari 488 has a rectangular engine air filter. In most ‘normal’ cars, they tend to live in a black plastic box in one of the front corners of the engine bay. Your car manual will point out exactly where it is, but you should be able to tell for yourself because it will have an intake tube that leads into the engine.
The best air filters at a glance:
Best paper filter for most VWs: Mann Filter C 30 005 - buy from Amazon.
Best cotton filter for small Fords: K&N 33-3117 - buy from Amazon.
Best air filter cleaning kit: K&N Air Filter Cleaning Kit - buy from Amazon.
Rectangular filters are generally made of either paper or cotton. Paper ones usually come with cars direct from the factory, because they are cheap and efficient.
How to find the correct air filter for your vehicle
Find the right air filter for your car
Via AmazonPros
- Many, many cars to filter
- Easy to use
Cons
- Free delivery isn't possible without Prime
Guide to air filters
Best for most VW-group cars
Via MannThere is a fair percentage of you who will own a car that this filter fits. This one suits some Mk 7 and 8 VW Golfs, and most modern Skodas, Seats, and small Audis.
Pros
- Easy to install
- Affordable
Cons
- Single use
Best for Minis
Via MannThis one meanwhile, is for most current Minis and some BMW models. In other words, quite a wide range of cars on the road.
Pros
- Easy to install
- Does the job
Cons
- Can't be cleaned like cotton filter
Best cotton filter for VW group cars
Via K&NUnlike paper air filters, cotton filters can be washed and reused. So while they are more expensive upfront than paper ones, they last far longer. The K&N cotton filters below claim to reach 50,000 miles before they require a clean. They tend to filter a bit more effectively than paper ones, too.
The cotton alternative fits most modern 2.0 and 1.6 litre from the VW Group.
Pros
- More durable than paper filters
- Easy to fit
Cons
- Only fits VW Group cars
Best for small Fords
Via K&NThis cotton filter fits a handful of modern Fords, including the Fiesta and EcoSport.
Pros
- Can be cleaned
- Good quality
Cons
- Only fits small Fords
Best performance filter for Fords
Via K&NCone filters are aftermarket pieces. You’ll be thinking about the engine bay of a Group B rally car or a touring car which house air filters the size wine barrels. Those who tend to fit cone-shaped air filters to their cars do so because they want higher airflow and more power.
Cone filters are quite vehicle-specific. This, for example, is a K&N cone replacement filter for a Mk3 Ford Focus ST.
Pros
- Easy to replace standard filter with
- Has a fairly cool look
Cons
- Don't expect more performance
Best air filter cleaning kit
Via K&NThe general rule of thumb is you should tend to your engine air filter once a year. A K&N filter may well do 50,000 miles between cleans, but you should check them annually regardless. When the time comes, paper filters simply get replaced, whereas the cotton ones you can wash – they also need re-oiling.
This kit has a spray that you apply to loosen grime before washing, and oil to apply to the clean filter.
Pros
- Helps clear out dirt and grime in air filters
- Little doses can be used
Cons
- A spray bottle would be easier to use
Best cabin filter for small Fords
Via MannCabin filters are also called pollen filters. Rather than filtering the air that enters the engine, these are for the air that flows into the cabin. Like engine air filters, these also get clogged over time and need replacing about once a year, or every 20,000 miles or so.
Activated carbon filters stop particles, and gases, and eliminates odours. This particular cabin filter fits small modern Fords - the Fiesta, Puma, and EcoSport.
Pros
- Helps keep the cabin air clean
- Affordable to replace
Cons
- Only fits small Ford models
Best cabin filter for VW Group cars
Via MannThe Mann FreciousPlus does the same as the activated carbon ones above, but will also prevent bacteria and protect against allergens. This specific one fits most modern 1.0 litre VW Group machines.
Pros
- Easy to replace
- Helps keep the interior hygienic
Cons
- Only suitable for small VW Group cars
How to replace your air filter
In tackling the actual job of removing air filters, it’s a piece of cake. Firstly, when the engine is cold, unclip and open the air box. Then you remove the filter inside and clean the empty air box. If checking the condition of the filter, make sure the filter is free from oil and dirt.
If washing a cotton filter, follow the filter manufacturer’s instructions. When putting in the new or cleaned filter, simply refit properly and pop the cover back on. Numerous YouTube videos will also guide you through the very quick process.
When it comes to cabin filters, they usually live behind the glovebox, your car manual should tell you exactly where. YouTube is an excellent tool here, and you will be able to find a video on how to replace the cabin filter on your car model. It’s a two-minute job that usually involves unclipping the glovebox so that it fully unhinges like a python’s jaw, behind which you will find the cabin filter. Pull the old one out, pop the new one in.
Aaron Hussain is a commercial content writer at Bauer Media writing for Parkers and CAR. He is obsessed with classic cars and anything with a fascinating story to tell.