Clean airways: CAR’s guide to air filters

You wear a mask now and know how gross it is inhaling through a dirty one. Attend to your car's air filters with our easy DIY guide.

Air filter in a blue car

by Chris Williams |

Peering into the plastic and metal guts of your car’s open engine bay, as a car enthusiast, you wish you could do more fettling and tinkering than refilling the washer fluid. Your dad used to spend whole Sundays under his Rover, after all. You too can get a slice of that action for about five minutes a year by, tending to your car’s air filters.

Function

No doubt you know that air filters do what they say: filter air. 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, yet are very simple to maintain and replace.

Air filter types

Air filter types: air filter on white background
©Photo: Getty Images

Let’s begin with the range of air filters, before we delve into maintenance.

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.

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.

Mann Filter C 30 005 Paper

Mann Filter C 30 005 Paper
Amazon

View offer

There 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.

Mann Filter C 22 018 Paper

Mann Filter C 22 018 Paper
Amazon

View offer

This one meanwhile, is for most current small BMWs - the 1, 2, X1, and X2. Also, it'll fit the current Minis.

On the other hand, 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.

K&N 33-3005 Cotton Filter

K&N 33-3005 Cotton Filter
Amazon

View offer

The cotton alternative fits most modern 2.0 and 1.6 litre from the VW Group.

K&N 33-3117 Cotton Filter

K&N 33-3117 Cotton Filter
Amazon

View offer

This cotton filter fits a handful of modern Fords, including the Fiesta and EcoSport.

Cone 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.

K&N E-2993 Air Filter

K&N E-2993 Air Filter
Amazon

View offer

Cone filters are quite vehicle-specific. This, for example, is a K&N cone replacement filter for a Mk3 Ford Focus ST.

Circular filters are still available but fitted to older, pre fuel injection cars.

Circular air filter
©Photo: Unsplash

Engine air filter maintenance

The 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.

K&N Air Filter Cleaning Kit

Top air filter cleaner
K&N 99-5003EU
Amazon

View offer

This kit has a spray that you apply to loosen grime before washing, and oil to apply to the clean filter.

You will need to find the air filter that is specific to your car. The part number on the engine air filter in your car will help find a replacement, otherwise, car parts websites and even Amazon will let you search by entering your reg number or car model details.

Amazon garage screenshot
©Amazon

In tackling the actual job of removing air filters, it’s a piece of cake:

1. When the engine is cold, unclip and open the air box.

2. Remove the filter inside and clean the empty air box.

3. 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.

4. 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 two-minute process.

Cabin air filters

These 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.

A cabin air filter will be more noticeable to you than an engine air filter. Once air from your air vents is no longer fresh, or your air conditioning is louder than what it was, it’s time for a new filter.

Find the correct cabin filter in the same way as sourcing the engine air filter above.

Mann CUK 2436 Cabin Filter

Mann CUK 2436
Amazon

View offer

Activated carbon filters stop particles, and gases, and eliminates odours. This particular cabin filter fits small modern Fords - the Fiesta, Puma, and EcoSport.

Mann FP 26 009 Cabin Filter

Mann FP 26 009
Amazon

View offer

The 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.

How to replace your cabin filter

Cabin filters 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.

READ NEXT:

The car owner's guide to windscreen wipers

The best engine oils

Best car battery chargers

Just so you know, whilst we may receive a commission or other compensation from the links on this website, we never allow this to influence product selections - read why you should trust us