Features of gasoline engines (BMW 5 Series E34)

When an over-rich fuel mixture enters the cylinders, or when the engine is rarely or never required to develop its full power, or when the engine is often operated in a cold state (short trips around the city), the consequence is incomplete combustion of fuel. Carbon deposits, oil carbons and other products, unburned fuel itself and moisture condensates cause the formation of sludge, acid and asphalt. Unburned fuel gets on the cold cylinder walls and flows down them into the crankcase, washing off the oil film from the cylinder walls and pistons. The consequence of this is deterioration of lubrication of the cylinder walls and dilution of the oil, affecting the lubricating properties of the oil depending on the amount of fuel that has entered the oil.

If the oil is very thin, it should be replaced early. Since with a sharp driving style (hot engine) gasoline particles evaporate in the oil, the oil level should be checked more often in winter (numerous cold starts - high proportion of gasoline in the oil).