What Causes Motorcycle Engine Oil to Turn Yellow?

[RafaelMarie]

Oil turning yellow is caused by poor oil quality or excessively low external temperatures. Poor Oil Quality: Poor quality oil can lead to yellowing. To protect the engine, it's advisable to use high-quality oil. Excessively Low External Temperatures: During winter, the significant temperature difference between the inside and outside can cause cold air to enter the crankcase through the balance hole after the motorcycle is parked. Since cold air contains some water vapor, it condenses into water upon cooling, resulting in oil-water mixing and oil emulsification. If this is the cause, after changing the oil, simply adding a filter at the balance hole can prevent recurrence. Otherwise, the oil will turn yellow again shortly after replacement.