What Are the Causes of Engine Abnormal Noise?
4 Answers
Engine abnormal noise causes: 1. Aging or loosening of engine mounts; 2. Excessive wear between pistons and cylinder walls; 3. Overly rich air-fuel mixture; 4. Air leakage in engine intake pipes; 5. Poor sealing of idle control valve; 6. Mechanical failure in the engine; 7. Excessive carbon buildup on throttle body; 8. Throttle body malfunction. An engine is a machine that converts other forms of energy into mechanical energy, including internal combustion engines, external combustion engines, jet engines, electric motors, etc. For example, internal combustion engines typically convert chemical energy into mechanical energy. The term engine can refer to either the power generation device or the entire machine including the power unit.
Last time my old Bora suddenly made a tractor-like clanking noise, and it turned out to be a worn connecting rod bearing after inspection. Engine abnormal noises can range from minor to severe: metallic knocking often indicates loose connecting rod bearings or crankshaft wear; a ticking sound is mostly due to excessive valve clearance or failed hydraulic lifters; if it's a hissing sound like sandpaper rubbing, it might be a stretched timing chain. Belt squealing is the gentlest warning, but a clattering noise should alert you to life-threatening issues like loose piston pins. The scariest is sudden engine knocking, where metal fragments can pierce through the cylinder. It's recommended to turn off the AC and slow down immediately at any strange noise—continuing to drive might directly scrap the engine.
Our auto repair shop commonly categorizes abnormal engine noises into three levels: Lightweight is the squeaking sound from a slipping timing belt, usually caused by belt aging or oil contamination; Mid-level is the popping sound resembling frying beans coming from the valve chamber, more noticeable when the engine is cold—adjusting valve clearance or replacing lifters typically solves it; Heavyweight is the dull knocking noise from the crankcase, most likely due to bearing wear, and the oil pressure warning light might not even illuminate yet. Last week, a modified car owner ignored the noise until the engine seized, with the connecting rod puncturing the oil pan—when towed in, engine oil was everywhere. In reality, abnormal noises are the engine's distress signals; listening to its complaints is far better than facing a hefty repair bill.
Novice drivers often overlook the early signs of engine abnormal noises. During rush hour traffic jams, if you hear a rattling sound resembling coins shaking in a tin can, it might indicate a stuck variable timing gear; the whistling sound during hard acceleration is likely caused by worn turbocharger bearings; the most subtle is the ticking sound of the charcoal canister solenoid valve, often mistaken for valve noise. My brother's car suffered from this – he thought valve noise was harmless, only to end up with stuck piston rings and oil burning. In fact, diagnosing an engine is like a traditional Chinese doctor taking pulses – the frequency of metallic knocking at idle and the tonal changes corresponding to throttle depth are all critical diagnostic indicators.
