What Causes the Abnormal Metallic Friction Sound in the Engine?

[OEmilio]

The causes of abnormal metallic friction sounds in the engine are as follows: 1. Valve noise: During cold starts, when both water and oil temperatures are low, if the viscosity and lubrication of the engine oil are insufficient, the tappet cannot adjust properly, resulting in metallic friction sounds during cold starts. 2. Hydraulic lifter: It could be due to the hydraulic lifter—either the oil pressure is too low or the lifter itself is worn. Once air enters the lifter, a metallic friction sound will occur when starting the car. 3. Front cover assembly issue: If the engine front cover is not properly installed, the output power increases during cold starts, leading to a corresponding increase in engine noise. This is normal, but if the noise is excessive, you can report this condition during maintenance.