What are the symptoms of a bad engine bearing?

[Theo]

Engine bearing failure exhibits noticeable symptoms such as bearing noise and bearing seizure due to dry friction. The details are as follows: Noticeable bearing noise: During cold starts under heavy load, the engine oil, being viscous at low temperatures, fails to lubricate the bearings in time. Meanwhile, the bearing surface reaches an instant high temperature due to the heavy load, causing metal fusion and seizure. Over time, as normal wear increases, the bearing clearance expands, leading to noticeable bearing noise. This results in oil loss and pressure drop, insufficient oil supply between bearings, high temperatures, and eventual fusion and seizure. Bearing seizure due to dry friction: Lack of coolant or prolonged high-temperature driving causes the engine oil temperature to rise rapidly, losing its viscosity. This prevents the formation of a protective oil film between the shaft and bearing, leading to severe friction, fusion, and seizure. Reduced oil pump pressure makes it difficult for the oil to reach designated lubrication points at standard pressure. Clogged oil screens or passages by contaminants block oil flow to the crankshaft, and oil leaks in the pipeline reduce lubrication system pressure, resulting in bearing seizure due to dry friction.