Over the winter, your car's air filter can get clogged with salt and other thick debris. A clogged air filter can really lower your fuel efficiency. Replacing a dirty or clogged air filter can improve gas mileage by as much as 10 percent.
But how do you know when to change your air filter? The recommended interval is every 12,000 miles (19,312 kilometers), but that can be affected by the particular road and air conditions in which you drive. If you do a lot of driving on dirt or gravel roads, then your air filter is going to clog up much faster than an air filter in a vehicle that's used strictly for highway driving. The only real way to know if you need to replace your air filter is take it out and give it a quick inspection.
Interestingly, a slightly dirty air filter works better than a totally clean one. This is because the debris in the filter becomes part of the filtering process, trapping smaller particles that might have otherwise slipped past.
There's no real science to knowing when it's time to replace the filter. If it's really filthy, then it obviously needs to be changed. Otherwise, go with your gut. If you're preparing for a long summer of hard driving, then you might as well replace it. Air filters are relatively inexpensive.
