What could be a visible indicator of a dirty air cleaner?

A dirty air cleaner can restrict airflow into the engine, which disrupts the ideal air-to-fuel ratio needed for efficient combustion. When the engine doesn't receive enough air, it can lead to a loss of power, especially during acceleration or when climbing hills. This diminished power output is often noticeable during everyday driving conditions, making it a clear indicator of an issue with the air intake system.

Dark exhaust smoke and excessive fuel consumption can also be related to air intake issues; however, they can arise from a variety of other problems, such as fuel system malfunctions or ignition issues. Vehicle stalling can occur due to numerous reasons, including electrical issues or fuel delivery problems, and while it might relate indirectly to the air cleaner, it is not a direct indicator. Therefore, a loss of power specifically ties back to the restricted airflow caused by a dirty air cleaner, making it the most relevant visible indicator.