What Causes the Abnormal Metallic Friction Sound in the Engine?
3 Answers
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.
Last time I encountered a metallic grinding sound from the engine, it was like metal scraping against a plate, especially more piercing during acceleration or cold starts. I've asked many mechanics, and they said this often stems from bearing wear, such as the water pump or crankshaft bearings becoming loose over time, producing a hissing friction sound. The belt system is another common culprit—if the drive belt is aged, too loose, or slipping, it can create abnormal noises by rubbing against the pulleys. Insufficient lubrication is also a major issue; oil leaks or oil pump failures can cause direct metal-to-metal contact and friction. There was also a case with my friend's car where the sound resembled scraping, and upon inspection, it turned out to be rusted exhaust system components rubbing together. Such problems should never be ignored—it's recommended to drive to a professional shop immediately for diagnosis, as delaying repairs could lead to engine damage, increased repair costs, or even safety hazards. During routine maintenance, regularly change the oil and inspect the belts to prevent small issues from turning into big troubles.
My car had that metallic scraping noise a while back, especially noticeable right after starting, and while driving it felt like something was scraping inside the engine. I took it to the repair shop, and the mechanic opened it up for inspection—turned out to be a belt issue. It had aged too much, causing friction and noise against the pulley. After replacing the belt, it became much quieter. But he also mentioned other possibilities, like a bad bearing or loose alternator components. If the bearing is rusted or worn, the sound can be very sharp. Lubrication is also crucial—insufficient oil increases friction, leading to squeaking. Another detail is a faulty fan clutch, which can cause grinding when stuck while rotating. If you hear this kind of noise, I’d advise against revving the engine hard. Shut it down as soon as possible to check the oil level or belt condition, and if needed, consult a professional before a minor issue turns into a disaster.
