When to change Air-Filter

How an Air Filter Works

The purpose of an air filter is to trap dust and debris so that it does not get into the intake system and potentially damage the engine.  While oldercarburetor-equipped cars use ring-shaped filters, most current air filters are rectangular in shape and made of a kind of pleated paper. This heavy pleated paper resembles felt more than it does writing paper and is surprisingly strong. The pleats increase the surface area of the filter, allowing more air to pass through than would otherwise be possible, ensuring the engine does not starve for air. It is a simple and effective piece of technology.

Other Kinds of Air Filters

The traditional paper air filter is not the only option for a car, but it is by far the most common. It is inexpensive, reasonably efficient, and readily available. However, the paper filter may not meet all drivers' needs, and so there are a number of alternatives available. Many off-road drivers use foam filters, which can trap more dirt than paper while still allowing air through. They are also easier to clean, which can be a benefit for people who go off-roading every weekend and do not want to replace the air filter after every trip. Another option is the oil-bath filter, which uses a combination of a filter mesh and a tub of oil. The air is routed through the two in order to remove any particulate matter or other debris that could harm the engine.

When Does an Air Filter Need Changing?

The thing to remember about changing an air filter is that the frequency with which they need to be changed depends primarily on the vehicle's driving conditions and then on the filter itself. Climate and road conditions both play a huge part in determining the lifespan of an air filter. People who live in a dry and dusty climate or who spend a lot of time driving on unpaved roads are going to need to replace their air filter more often than someone who drives primarily on paved roads and lives in a wetter climate where the rain tends to wash most of the particles out of the air.

Symptoms of a dirty air filter include lack of power on hard acceleration and at higher RPMs. A clogged air filter won't significantly affect fuel economy, according to a 2009 study conducted for the U.S. Department of Energy, but it can hurt acceleration by 6% to 11%, although it's not always noticeable to a casual driver.
Instead, many people use a visual inspection to determine whether they need to change the air filter in their car, working on the principle that if it does not look clean, it needs to be changed. Unfortunately this is not always the case, as sometimes a filter actually begins to work better with some dust since it helps trap particles of a particular size. Some trucks rely on a "restriction meter," which actually serves to measure airflow and let the driver know when the filter needs replacement. For those who do not have such a meter, the visual inspection is the best way to go, but the key is to visual inspection is knowing what to look for.

There's an element of guesswork and differences in visual inspection, but the following table provides tips for judging whether an air filter needs replacement or just cleaning:

Condition	Change or Clean
Clean and White	No
Slightly Dirty	No, most efficient
Thin Layer of Dirt	Clean
Caked With Dirt	Change

Following these guidelines helps ensure the best performance from any vehicle.

Changing Air Filters on a Schedule

Not everyone wants to rely on their own visual inspection to determine when to change their air filter, so they prefer to rely on a set of guidelines because different people have different interpretations of the difference between a thin layer of dirt that can be readily cleaned from the filter and enough dirt that it has caked into the filter, causing a restriction of airflow with a commensurate decrease in horsepower and performance. For these people, the following guidelines may be more helpful.

Change the Air Filter With Every Other Oil Change

This is a simple guideline to follow, especially for those who live in dry and dusty climates. By tying the air filter change to another form of regular maintenance, it becomes much easier to remember when it needs doing and ensure that it gets done properly. It makes sense to tie it to the oilchange because the need for both changes are often driven by the same conditions. Car manufacturers generally recommend an oil change after every 30,000 miles driven. A vehicle that is regularly driven in an area with lots of particles in the atmosphere often needs more frequent oil filterchanges as well as air filter changes.

Change the Air Filter Every Year

Another option is to change the filter every year. As with tying it to oil changes, this provides a simple way to remember when the filter needs changing. This method works very well for someone who does a lot of city driving, where the relatively clean streets often mean less dust or other debris in the air. Someone who lives in a more rural area may find that an annual change is not frequent enough, as their vehicle picks up too much dirt in the filter.

Changing Air Filters by Distance Driven

Depending on the source, air filters should be changed at intervals of every few thousand miles to every 60,000 miles, whether they need it or not. Obviously, with such a wide variety of recommendations, it can be hard to find a clear consensus. One reason for this may be as simple as the fact that air filter technology has advanced over the years and with it the interval between changes. On the balance, though, it can be hard to argue with the idea that the filter should be checked at least once a year, or every 10,000 miles. While this may not be perfect, it provides a good guideline for those who want to base the change on mileage.

Changing High Performance Air Filters

Some drivers use high-performance filters, which have less restriction and thus provide more horsepower. While this can be a benefit, these filters do provide less protection for the engine against dust and debris and so should be used with caution. For most drivers, the cost of engine repairs are likely to outweigh the benefits of a few additional horsepower.