Why is the engine noise loud during cold start?

[DiReed]

Engine noise being loud during cold start is a normal phenomenon. If the engine sound is relatively loud during cold start but becomes quieter after about one minute, and the noise is much lower during warm start, this is considered normal. This occurs because after parking, the engine oil automatically flows back to the oil pan. During the next cold start, the oil will gradually return from the oil pan to the vicinity of the cylinder head. The following are hazards of an excessively cold engine: 1. The temperature of the air-fuel mixture (or air) entering the cylinder is too low, resulting in poor combustible mixture quality, making ignition difficult or combustion delayed, leading to reduced engine power and increased fuel consumption. 2. Water vapor in the combustion byproducts tends to condense into water and combine with acidic gases to form acids, intensifying corrosion on engine components and parts. 3. Unvaporized fuel washes away and dilutes the oil film on part surfaces (cylinder walls, pistons, piston rings, etc.), accelerating part wear.