Why does the car make a rattling noise when starting?

[EverettFitz]

This is caused by the engine oil temperature being too low and the ambient temperature being too low. When the engine oil temperature is too low, there is insufficient lubrication between the various components inside the engine. At this time, the friction between the components is relatively high, resulting in some abnormal noises. Engine oil primarily has three functions. Lubrication and friction reduction: It forms an oil film on the surfaces of two sliding components, preventing friction during operation and ensuring smooth movement of the components. Auxiliary cooling: When the engine is running, it generates high temperatures. When the oil reaches the operating parts, it absorbs heat and carries it away, aiding in the dissipation of heat from the components. Cleaning: It can carry carbon deposits, sludge, and worn metal particles from engine parts back to the oil tank through circulation. The flow of the lubricating oil washes away dirt generated on the working surfaces of the components.