When you go in for an oil change at some point you have probably had the mechanic tell you it’s time to replace your engine air filter. Before ignoring his advice and declining to purchase a new one, find out why a clean air filter is important.

A functioning air filter helps extend the life of an engine by preventing contaminants from entering it. This also helps the engine perform better and more efficiently.

To ensure your air filter is working properly you should change it every 15,000 to 30,000 miles, according to Ford.

Drivers who often drive on dirt roads, or for those who feel their car isn’t driving as well as it used to, might want to consider changing their filter more often.