What Causes Blue Smoke from a Heated BMW 7 Series?

[PeterLee]

Blue smoke from the car is caused by incorrect oil viscosity selection, carbon buildup on piston rings, aging valve seals, and other reasons. The specific causes are as follows: Incorrect Oil Selection: Manifested by no blue smoke during cold starts in the morning, but a small amount of blue smoke appears after the engine warms up. There was no blue smoke before, but it appears after switching to another type of oil. The car accelerates normally, but oil consumption is excessive, and engine noise increases. Carbon Buildup on Piston Rings: Carbon buildup causes the piston rings to lose tension, resulting in poor sealing. Oil enters the combustion chamber through the gaps. Power output decreases, cylinder compression and sealing performance decline, and oil consumption relatively increases. Aging Valve Seals: Hardened valve seals cannot expand and contract with temperature changes, allowing oil to enter the combustion chamber during cold starts. A stuck PCV valve allows combustible mixture to enter the crankcase, thinning and degrading the oil, which then enters the combustion chamber and accelerates oil consumption.