Air Filters: How often should they be changed?

The other day a customer dropped her car off at our shop for an oil change. She was confused when we told her the car needed a new air filter. "Didn't you just replace it in November?" Yes we had, but some mice had moved in for the winter and had filled it with sunflower seeds, hair and mice droppings. Unfortunately this is a common occurrence in Vermont. Those pesky mice enjoy a warm engine during the cold winter season.

Most cars need to have the air filter changed between one or two times a year, or roughly once every 12,000 to 20,000 miles. Why such big parameters? It depends on how quickly the air filter in your car gets dirty. If you do most of your driving in a dusty or sandy area, you might need to replace your air filter every 5,000 miles or less.

You may be wondering why I'm giving the lowly air filter so much attention. It's only a beefed up version of a paper coffee filter for Pete's Sake! Simple as it may be, this filter has a critical job. It cleans the air coming into the engine, and stops debris such as dirt, dust, leaves and wayward mice before they get inside the engine and do damage.

Replacing your air filter could help you save $100.00 a year. Seriously!

When the air filter begins to get clogged with dust, the air flow into your engine slows down and your automobile quickly becomes less fuel efficient. A dirty air filter won't allow your engine to suck enough air into the combustion chamber. The engine will then run "rich" (i.e., too much gas and not enough air). When this happens, your car will lose power and run less efficiently. The Department of Energy claims that replacing a clogged air filter can improve fuel efficiency by up to 10%. That's about thirty cents on every gallon of gas. If you are driving a car that normally gets 25 miles per gallon, your dirty air filter may be causing your car to get only 22.5 MPG. Over the next 15,000 miles, that's an extra 66 gallons of gas. Multiply this with the cost of gas at $2.60 per gallon, and you would lose over $173.00.

Could anyone do it? Sure you could. But it's not an expensive job and it gives your auto technician a chance to look over the engine, belts, hoses and fluids while they are under the hood. If you really want to D.I.Y., please make note of these important points before you roll up your sleeves and don your baseball cap.

  • Each vehicle needs its own specific filter. It is imperative that you make sure you get the correct filter for your car's year, make and model. Make sure that the new filter you purchased matches your old filter in size and shape. If it doesn't, you have the wrong one. NO, don't use it. It needs to be exactly the same. Go back to the parts store and get the correct filter.
  • Don't skimp on the quality of the filter. Purchase a quality-brand filter. You may find that a cheap filter is very costly in the long run.
  • Where the air filter is located will be determined by if you have an older car with a carbureted engine or a newer car with a fuel-injected engine. The air filter in a carbureted engine is round in shape and lives under a round metal piece that's usually about the size of a medium pizza and sits at the top-center of the engine. The air filter in a fuel-injected vehicle is located in a black plastic casing the size of a breadbox. It can be near the center-top of the engine or be off to the side. The fuel-injected filter is usually a flat rectangle, about a foot long by six inches wide by two inches high. It's made of paper filament, with rubber edges along the bottom to seal it against the casing. It comes in a variety of colors: yellow, orange or red.
  • Make a sketch of the air filter box and everything that is attached to it. You will NEED to reconnect everything that you disconnected. If you miss anything you could do damage to your car!
  • Make sure you don't put the filter in upside down and make sure it seals properly.
  • When you are reconnecting the air box, be careful not to over tighten the holding screws.

Remember, spending a few dollars on a new air filter now can save you hundreds in fuel costs. Next to changing your oil and oil filter, replacing your air filter on a regular basis can have a significant impact on engine life and performance. It is one of the simplest, least expensive and most important maintenance procedures you can perform on your car.

Happy Motoring,

Amy