Why a Dirty Air Filter May Not Hurt Engine Performance

Every oil change, the service advisor offers the same recommendation. "Your air filter looks dirty. We should replace it. It"s cheap and it will improve your engine"s performance." The recommendation seems perfectly logical. A dirty filter must restrict airflow. Restricted airflow must reduce power. Clean air is essential for combustion. Therefore, a clean filter must be better than a dirty one. This logic is so simple, so intuitive, that almost no one questions it. The logic is also wrong.