Engine Air Filter Replacement: When Does It Need Doing?

Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent

Engine air filter replacement is usually done at the intervals in your car’s service schedule, often every other service or with a full service. Haynes gives a typical range of 40,000 to 60,000 km (roughly 25,000 to 37,000 miles) or every two to four years, but it varies by car. Dusty roads and lots of short town trips mean it may need doing sooner, so check your handbook or service book.

What the engine air filter does

Your engine needs a steady flow of clean air to burn fuel properly. The air filter sits in a plastic box in the engine bay and catches dust, grit and debris before the air reaches the engine.

Haynes explains that unfiltered air carries abrasive dust that wears the cylinders, pistons and piston rings. A good filter is cheap protection for some of the most expensive parts of the engine.

This is a different part from the cabin or pollen filter, which cleans the air coming into the car for you to breathe. If that is what you are after, see our guide to cabin filter replacement.

How often should it be replaced?

There is no single answer. Each manufacturer sets its own interval, and some ask for an inspection rather than a fixed swap.

• Service schedule: Haynes says the air filter is generally replaced every other service, with a typical range of 40,000 to 60,000 km or two to four years.
• Full service: The AA lists air filter replacement as part of a full service, but not an interim service.
• Clean driving: AAA, the American motoring organisation, says a filter used mostly on clean city or suburban roads may last 20,000 miles or more.
• Harsh conditions: Both Haynes and AAA say dusty or rural driving calls for shorter intervals. Haynes adds short urban trips to that list.

AAA also points out that replacing the filter more often than needed wastes money for no real benefit. A light layer of dust actually helps a filter trap dirt better.

Signs your air filter may be clogged

A blocked filter rarely causes dramatic symptoms. Things to watch for include:

• Weaker acceleration. AAA says a badly restricted filter reduces the engine’s maximum power.
• Rough running or stalling. The AA says a clogged air filter can restrict airflow, upset the air and fuel mix and cause the engine to stall.
• A filter caked in dirt when you lift the lid of the airbox.

These signs can also come from many other faults, such as ignition or fuel problems. If your car is stalling or running badly, get it diagnosed rather than assuming it is the filter. Stalling at a junction or on a busy road is dangerous, so stop driving it until it has been checked.

Does a dirty air filter hurt fuel economy?

This is a common myth. The US Department of Energy’s fueleconomy.gov site says replacing a clogged air filter on a modern fuel-injected petrol or diesel car does not improve fuel economy, but it can improve acceleration.

Older carburettor engines are different. The same source says a new filter on a carburettor car can improve both fuel economy and acceleration by a few percent. That makes the air filter more important on classic cars, which we work on regularly.

How to check your air filter

On many cars the airbox is easy to reach. It is usually held shut with clips or a few screws.

AAA suggests a simple light test for pleated paper filters. Hold the filter up to a bright light. If light passes easily through more than half of it, it can stay in for now. Dense fabric extended-life filters often block light, so follow the manufacturer’s mileage interval for those.

When a new filter goes in, Haynes says to check three things:

1. The housing is clean before the filter goes in.
2. The filter sits correctly and follows the airflow arrow printed on it.
3. The lid seals fully all the way round.

Haynes warns that a badly seated filter lets unfiltered air through, which can cause noise and engine problems. If you are not confident, leave it to a mechanic.

What affects the cost

The job itself is often quick. Haynes rates it as one of the easiest maintenance jobs, at around 10 to 20 minutes on a typical car. The cost mainly depends on:

• The price of the correct filter for your make and model.
• How easy the airbox is to reach. Some engines have covers or pipework in the way.
• Whether it is done alone or as part of a service, which saves on labour.

We do not quote fixed prices for parts, as they vary so much between cars.

How we can help

We replace engine air filters at your home or workplace, either on their own or as part of an interim or full service. We cover Aylesham, Canterbury, Dover, Deal, Sandwich, Folkestone and the villages in between. See all the areas we cover.

Labour is £30-£50 per hour depending on the job, and we agree the price with you on WhatsApp before any work starts. Parts are extra. If your car has other servicing due, our car service checklist shows what is worth doing at the same visit.

We also service classic and vintage cars, where a clean air filter matters even more on carburettor engines.

Frequently asked questions

Is the engine air filter the same as the pollen filter?
No. The engine air filter cleans air going into the engine. The cabin or pollen filter cleans air coming through the vents into the car.

Can I drive with a dirty air filter?
A slightly dirty filter is normal and still works. A badly blocked one can reduce power and, according to the AA, can cause stalling. If the car is stalling, stop driving it and get it checked.

Will a new air filter save me fuel?
On a modern fuel-injected car, fueleconomy.gov says no, though acceleration may improve. On an older carburettor car, it can help a little.

Should the air filter be changed at every service?
Not usually. Most schedules replace it every other service or at set mileages. Check your handbook or service book.

Need help? Send a WhatsApp to 07563 350335 with your car’s make and model and we’ll come to you.

Sources

• Haynes: How to change the air filter on your car
• AAA: Changing your car’s engine air filter
• fueleconomy.gov (US Department of Energy): Keeping your vehicle in shape
• The AA: What’s included in a car service?
• The AA: Why is my car engine stalling?