What Causes Engine Noise When Cold?
1 Answers
Cold start engine rattling occurs because after a car has been parked for a day, the engine's lubricating oil has mostly flowed back into the oil pan. Below are the reasons for engine noise during cold starts: 1. During a cold engine start, the oil pump cannot immediately establish oil pressure and form an oil film between components, especially the valves inside the cylinder head (upper part). Without lubrication during a cold start, both hydraulic lifters and mechanical rocker arms will have some valve clearance, leading to a rattling sound. After the engine runs for a while, oil pressure builds up, the oil film forms, and the oil temperature rises. Once the engine operates normally, the "rattling" sound disappears (note: if the engine continues to make rattling noises when hot, have it checked at a repair shop as soon as possible). 2. Apart from oil-related issues, another component that can cause a rattling sound is the carbon canister purge valve. Its function is to open the solenoid valve between the carbon canister and the intake manifold after the engine starts, allowing the gasoline vapors adsorbed by the carbon canister to be drawn into the cylinders by the vacuum in the intake manifold for combustion. This not only reduces emissions but also lowers fuel consumption. During operation, the purge valve can also produce a rattling sound.
