The exhaust gas in the crankshaft is sucked into the valve cover for filtration, and then enters the intake pipe into the cylinder to participate in combustion again. Judging from the composition of BMW’s valve cover, it is not impossible to even lack this oil and gas filtration ability. Moreover, the vaporization of engine oil in the crankshaft exhaust gas is extremely limited, because the boiling point of engine oil is above 150 degrees, while BMW’s engine oil temperature is within 100 degrees, so almost no oil gas is produced.
Therefore, many analyses on the Internet are completely wrong and blindly follow the rhythm. At present, it is generally believed that if there is oil in the spark plug, it will be said that the oil is burned, and if there is carbon deposit in the spark plug, it will be said that the carbon deposit in the cylinder is serious. However, BMW has not found any complaints about cylinder pulling caused by burning oil in the 5 Series and 3 Series series.
So focus on analyzing where the spark plug oil comes from? Please ask professionals from all walks of life to speak freely.
Judging from everyone’s feedback, most of them have oil on the threads of the head of the spark plug. If engine oil enters the cylinder and burns, it is almost impossible. How can the huge power of combustion in the cylinder keep the oil on the spark plug???
If it leaks in from the top of the spark plug, it doesn’t explain why there is no oil on the top of the spark plug and no oil on the ignition coil. The biggest personal feeling is that because the crankshaft ventilation device is close to the spark plugs of cylinders 1 and 2, a small amount of oil and gas that is not filtered at high temperatures is printed through the valve cover to the threads of the spark plug. This is a condensation of the mixed gas and not only contains a small amount of oil and a small amount of gasoline. Moreover, this amount is very limited or even negligible.
Professionals are welcome to discuss! If you are inappropriate, please correct yourself!

Add: Why can’t the oil in the spark plug be oil that enters the cylinder and then splashes on the spark plug? First of all, the combustion environment in the cylinder does not allow and cannot have this kind of existence. Any engine oil gas entering the cylinder will inevitably be burned instantly. Secondly, you can search the previous posts when the Volkswagen Audi ea888 burned engine oil. They burned engine oil so seriously, the spark plug is also dry, which can completely prove it.