What Are the Causes of Engine Idle Noise?
2 Answers
Here are the causes of engine idle noise: Piston Slap: Piston slap is a common source of abnormal noise. Due to poor lubrication conditions, excessive wear occurs between the piston and cylinder wall, causing the clearance tolerance between the piston and cylinder wall to exceed the normal range. During engine operation, the piston skirt impacts the cylinder wall, producing a crisp "clanking" sound. This is usually more noticeable during idle or low-speed operation. Timing Gear: After prolonged use, coupled with improper gear clearance adjustment and poor lubrication conditions, timing gears can experience excessive wear. In severe cases, the gear teeth may even become worn down, leading to loose meshing between gears. When the engine runs, this produces a "whirring, clattering" sound. Piston Pin Noise: Due to excessive wear of components, the clearance between the piston pin and connecting rod bushing becomes too large, the fit between the connecting rod bushing and small-end bearing becomes loose, and the clearance between the piston pin and piston pin bore becomes excessive. This causes the piston to wobble during movement, colliding with the cylinder wall and generating abnormal noise.
I have a five-year-old car that always makes a strange buzzing noise when idling, which worries me a bit. After researching and consulting with a mechanic, I learned that common causes include worn or loose drive belts, especially noticeable during cold starts; aging water pump or alternator bearings, which produce a continuous buzzing noise; internal engine issues like excessive piston clearance or knocking, which sound like metal clashing; and insufficient lubrication, which increases component friction. Ignoring idle noise is dangerous—for example, my colleague ignored the noise, and the engine eventually failed. It's recommended to check oil levels and belt conditions immediately upon noticing any sounds. Regular maintenance, like frequent oil changes, can prevent issues. Addressing small problems early saves money and hassle, avoiding major repairs later.
