How a car’s air filter works

A car’s air filter stops dust, debris and pollen from entering your engine, helping it to run cleanly and efficiently. Modern fuel-efficient engines are hi-tech pieces of kit that mix precise ratios of air and fuel to achieve optimum performance and economy. This places increasing demands on filters to supply clean air to the combustion chamber.

The latest air filters claim to block up to 96 per cent of debris, and most are made of a paper-type fibre with accordion pleats that increase their surface area to trap as much debris as possible.

Air filters may be hidden away inside a housing, but checking and replacing them if necessary is one of the easiest and cheapest car maintenance tasks that can be done.

And it’s money well spent, as a clean air filter can prolong the life of your car’s engine.

What is the lifespan of an air filter?

Whether your car is petrol or diesel, one fact remains – it needs air. Both fuels have to mix with oxygen in order to be at their operational best. Without air, your engine will cough, splutter and die.

But it has to be clean air. It’s sucked deep into the combustion chamber of your engine, so it has to be free of debris. If not, that debris will damage your engine, usually irreparably.

Of course, the carmakers have thought of this, which is why you’ll be confronted by a big black plastic box under the bonnet of every car. In this box sits the air filter, which collects all the dust, dirt and grim lingering in the atmosphere, stopping to from playing havoc with your engine’s internals. But how long do these filters last?

In theory, you could leave the same air filter in your car for years. It’s never going stop blocking the dirt and grim. Simply by being there, it’s doing something. However, if you do leave it too long, you’re going to find the filter gets so clogged it doesn’t let enough air through. As such, you really should change your air filter once a year at a minimum.

Changing it is easy and cheap, with most filters being about a tenner, while the costliest ones can about twenty quid. You normally have to contend with nothing more than a few spring clips, take the old one out, put the new one in, job done. It’s that simple.

If you live in a city centre, you may need to change your filter more frequently. Take a picture of your new filter for ref, then compare it to six months of use, if it looks significantly darker/dirtier, fit a new one.

The other option would be to upgrade the filter. You can buy performance air filters that are a direct fit replacement for the originals. These filters will let a bit more air through, while still keeping dirt and debris at bay. They can help with performance and in some cases, they can be washed/cleaned out and re-oiled, making them as good as new.

When to change your air filter

Most manufacturers recommend that air filters are changed every 15,000 to 30,000 miles. However, the frequency depends on the conditions your car has encountered, and how hard it is driven.

For example, if a car is used frequently during a long, hot summer, when dry air is laden with dust and pollen, the filter risks clogging more rapidly. It’s the same story if a car is driven regularly in polluted cities, or areas where a lot of construction work is taking place.

The lifespan of an air filter will also be significantly reduced if a car is regularly driven along dirt tracks. In such circumstances, it’s worth inspecting the air filter every six months or so, and replacing it if it looks the worse for wear.

There are warning signs that should not be ignored: a dirty, clogged air filter can result in a lack of power during hard acceleration and fuel economy may be slightly reduced.

If the air filter is seriously blocked or damaged, a service indicator or engine check warning light can appear on the dashboard.

How to change your air filter

Here's an example of how it's done

All cars are different, but here’s a summary of the job:

  1. Open the bonnet and locate your car’s air filter housing unit.
  2. Release the retaining clips, or use a screwdriver to undo the screws, and lift up the lid of the air filter housing.
  3. Lift out the old filter and dispose of it.
  4. Use a clean cloth to wipe any debris from the air filter housing.
  5. If the housing is very dirty, it’s worth using a vacuum cleaner to suck debris out.
  6. Insert the new air filter, making sure it’s fitted the correct way up.
  7. Refit the air filter lid and secure it in place by refitting the screws.
  8. Close the bonnet.

Why you should change your air filter

If air filters become clogged or damaged over time, the engine won’t be able to breathe properly – reducing your car’s performance and lowering fuel economy - and you risk debris being sucked into the engine.

Ingested contaminants have an abrasive effect once they have entered your engine, accelerating the rate of wear on vital components.

Over time, this risks damaging vital and expensive components of your engine, such as the valves, piston rings and cylinders.

Tools you may need

Changing an air filter is a basic job and you’ll only need a few tools, depending on the location of your car’s filter. We would suggest:

  • Flat-bladed screwdriver
  • Phillips screwdriver
  • A clean cloth (to wipe dirt from the air filter housing)
  • A vacuum cleaner (to suck debris from the air filter housing)

Parts you will need

  • Air filter. Always buy the correct filter for your car. It’s worth buying a quality brand of filter as it’ll help to keep your engine running at peak efficiency.

How much does an air filter cost to change?

Air filter £12-50
Garage fee savings £50-100