Car air filters: the expert’s guide

Changing your air filter is way easier than you might imagine. Very satisfying once you know how, and saves you money in the long run.

Air filter maintenance

by Chris Williams |

Tending to the air filters in your car is one of those DIY things that is hugely satisfying. It's easy, yet feels like you're digging deeper into the nitty-gritty of your car. Read on to learn everything you need to know about air filters, plus how to change yours and the best ones to buy.

What do they do?

Air filters possess a very apt name. There is no ambiguity about what they do. They filter the air that is fed into the engine that ultimately helps power your car. Car trivia fact for you: for every kilogram of fuel your engine burns, it needs around fourteen kilograms of air. You can take that knowledge to the pub (when they reopen).

An air filter keeps the air clean and protects your engine from swallowing and building up harmful debris. Air filters do need to be replaced every so often, but you can usually clean them yourself to prolong their life. Keep reading for our full tips on maintenance.

Types (shapes and materials)

You will find that effectively all modern cars have rectangular air filters fitted as standard. These live in a little air box in the engine bay, often one of the front corners. Your car manual will tell you where it is, and you should be able to spot it yourself because it will have an intake tube that leads from it to the engine.

There are other shapes of air filters kicking around, though. A lot of aftermarket performance air filters are a conical shape and many older, pre-fuel injection cars had circular air filters that sat on top of the motor. We aren’t going to focus on these two types here, rather the standard air filters in modern cars.

What is my engine air filter made of?

Paper, cotton, metal, or foam. Paper and cotton are the two most commonly found in standard and replacement rectangular air filters.

Paper

Most often, the standard air filter your cars comes with from the factory is a paper filter. They are inexpensive and do a good job. However, they aren’t able to be washed and simply get replaced once they’re used.

Mann Filter C 30 005 Paper

Mann Filter C 30 005
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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
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This one meanwhile, is for most current small BMWs - the 1, 2, X1, and X2. It also fits current Minis.

Cotton

Cotton is just as common a replacement as paper, if not more so. They are more expensive than paper ones to buy, but unlike paper filters, they can be washed when dirty. The K&N cotton filters below claim 50,000 miles before you need to clean them. It’s a money-saving exercise over time.

K&N 33-3005 Cotton Filter

K&N 33-3005 Cotton Filter
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This 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
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This cotton filter fits a handful of modern Fords, including the Fiesta and EcoSport.

Replacement and maintenance

The mileage claimed by the air filter manufacturer and the recommended mileage for replacing or cleaning air filters in your car’s manual may vary. The general rule of thumb is to replace a paper filter or clean a cotton one every year. At the very least, inspect it to check the condition. If you do low mileage, filters won’t necessarily have to be changed annually.

When the time comes to replace the filter, you need to find the one specific to your vehicle. The product number on the filter will help you find a replacement. Alternatively, there are online car parts websites which allow you to put in your car’s reg or model details and then present the filters that will fit. You can also do this on Amazon.

Amazon garage screenshot
©Amazon

Cotton filters need to be re-oiled after cleaning. There are filter cleaning kits available, such as the one below, that come with a cleaner to loosen dirt before washing, and oil to apply to the clean filter.

Replacing or servicing your air filter is an easy and satisfying job, you don't even need a screwdriver. There are numerous YouTube videos that will guide you through the process; below are the simple steps:

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.

Cabin air filters

The other kind of filter you’ll find in your car is the cabin filter – often called a pollen filter. As you would probably guess, these filter the air that flows into the cabin. Like engine air filters, these build up with dust and need replacing about once a year.

A clogged cabin air filter will be more noticeable to you than the one for your engine. If you notice the air from your air vents is no longer fresh, and perhaps your air conditioning is louder than what it was, it’s time for a new cabin filter.

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

Mann CUK 2346 Activated Carbon Cabin Filter

Mann CUK 2346
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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 FreciousPlus cabin filter

Mann FP 26 009
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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 it is.

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 snake’s jaw, behind which you will find the cabin filter. Pull the old one out, pop the new one in.

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