Mud and debris under the oil filler cap

Light-colored deposits (emulsion) under the oil filler cap indicate insufficient moisture in the engine oil. They often occur when driving continuously with a cold engine, especially during the winter months. The condensate accumulates in the engine over time, and the oil turns into a light beige emulsion. When the block seal burns out, the coolant can get into the engine oil, which ultimately leads to the formation of an emulsion.

Dark brown tar deposits indicate heavy contamination of the oil system.