What does it mean if a car engine is "knocking"?

When an engine is described as "knocking," it usually indicates abnormal combustion within the engine's cylinders, which can lead to engine damage if not addressed. This knocking noise often results from a condition known as "detonation," where the air-fuel mixture ignites prematurely or in an uncontrolled manner. Such abnormal combustion can cause excessive pressure and temperature in the combustion chamber, leading to potential wear or damage to engine components like pistons, connecting rods, and cylinder heads.

While low oil levels, exhaust system issues, or problems with spark plugs can certainly affect engine performance and health, these conditions do not specifically result in the characteristic knocking sound associated with detonation. Recognizing knocking as a sign of potentially severe combustion issues is crucial for maintaining engine longevity and ensuring safe vehicle operation. Thus, identifying knocking as an indicator of abnormal combustion or engine damage is crucial for diagnosing engine problems effectively.