What happens when the air filter is clogged?

When the air filter is clogged, it restricts the flow of air into the engine. This lack of adequate airflow affects the combustion process, leading to a richer fuel mixture, or a "thicker" gas mixture. A proper air-fuel mixture is essential for efficient engine performance; if the air supply is compromised, the engine cannot burn the fuel as effectively, which can lead to increased fuel consumption and potential performance issues.

The other options do not accurately reflect the effects of a clogged air filter. A clogged filter does not cause the engine to run cooler; in fact, it can lead to overheating due to poor combustion. Fuel efficiency would not improve; instead, it usually declines because the engine struggles to work efficiently with the incorrect fuel mixture. Finally, rather than more air entering the engine, a clogged air filter limits the airflow, which is detrimental to the engine's performance.