Clogged air filter means restriction of airflow to the engine, negatively affecting its performance. For every gallon of gasoline burned, an engine takes in about 9,000 gallons of air, which contains abrasive dust that may end up in the oil and cause damage. A clean air filter removes abrasive dust, insects and leaves from the air before it enters the engine. These contaminants cause excessive wear to moving parts. By allowing the correct mixture of air and fuel, a clean air filter will provide maximum gas mileage and better engine performance.

Regardless of the mileage or time, a filter should be replaced before it reaches the point where it creates a significant restriction to airflow. But when exactly that point is reached is subject to opinion.

A slightly dirty filter actually cleans more efficiently than a brand new filter. That’s because the debris trapped by the filter element helps screen out smaller particles that try to get through. But eventually every filter reaches the point where it causes enough of a pressure drop to restrict airflow. Fuel economy, performance and emissions begin to deteriorate and get progressively worse until the dirty filter is replaced.

Many heavy-duty trucks have a “restriction” meter on the air filter housing that signals when the filter is dirty enough to need replacing. But lacking such a device, the best you can do is guess.

Removing the filter and holding it up to a light will show you how dirty it is. If it’s really caked with dirt, it obviously needs to be replaced. Trying to shake or blow the dirt out is a waste of time because too much of it will be embedded in the filter fibers.

NOTE: Many filters that appear to be dirty are in fact still good and do not really need to be replaced. So it’s up to you. If you think it’s dirty, replace it. If you don’t think it’s dirty enough to need replacing, then don’t.

Jason Embleton, owner of Embleton Auto Ltd. in Fredericton New Brunswick, is an expert in the automotive industry. The Embleton family has served their customers since 1966 with the best deals in Fredericton used cars. Check out our site: http://www.embletonauto.com