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How to check and change your car’s air filter

About the author

Rob Keenan is the interim digital editor of Haynes.com
He runs a Mk2 Ford Focus ST and an ageing Mercedes SLK55
Find him on Twitter @zorba_t_greek

when change air filter car

Wondering when to replace your car's air filter? Unsure how it differs from your car's cabin filter, also known as a pollen filter? Perhaps you're just trying to find out what air filter your car needs. Haynes has the answers.

Your car's engine takes in air as part of the combustion process, but that air needs to be free of particles such as dust and leaves. If not, the engine – and the cylinders and pistons in particular – could be damaged.

This is why an air filter is used. It's usually made from either paper or a mixture of paper and cotton, although aftermarket 'performance' filters, such as those made by K&N, Pipercross and BMC, use foam coated in a thin layer of oil to allow more air to pass through. Most filters are square or rectangular but some are round. The filter sits within a housing under the bonnet.

Learn more about your air filter here

How often should an air filter be changed? With the exception of high-performance air filters, which tend to have a longer life, most air filters should be changed once a year, or after around 15,000 miles. It's easy to forget, so make a note of when you change it so you remember next year.

 

Watch this to see how to replace your car’s air filter

Every Haynes manual shows you how to change your vehicle's brake pads in easy-to-follow steps

 

Does your car’s air filter really need to be changed once a year? Can't you just leave it another year or just not change it at all? As mentioned, a lot depends on how many miles you cover but also on where you drive.

For example, if you're in a rural part of the country where the roads are often dusty and there's lots of tree pollen and hedgerows, you may find that the air filter is pretty dirty before 12 months have passed. If you live by the sea, where the air tends to be cleaner, the filter could look as good as new after a year.

Basically, it's best to use your common sense and not to let the filter get as filthy as the one pictured at the top of the page.

Learn more about how to change your vehicle's air filter – including where to find the air filter, the tools you need for the job and how much a typical air filter costs (as well as save you in garage fees) – here

We've saved the best bit until last, because checking and changing your air filter is one of the easiest and cheapest maintenance jobs you can carry out on your car. In many cases it's easier to change than the cabin filter.

The latter is often tucked up behind the glovebox and filters the air before it comes through the cabin's air vents, removing pollen and even exhaust particulates.