What is a common cause of oil foaming in an engine?

Oil foaming in an engine is often a result of a high oil level. When the oil level exceeds the recommended capacity, it can create turbulence in the oil sump. This turbulence can incorporate air into the oil, leading to the formation of foam. Foamed oil loses its effectiveness as a lubricant, which can result in inadequate lubrication of engine components and potential engine damage.

While using high-grade oil generally provides better lubrication properties, it does not inherently cause foaming. Oil being too cold may affect its viscosity and flow characteristics, but it is less likely to produce foaming unless combined with other factors. Water contamination is a significant issue for engine oil, but it typically leads to emulsification rather than foaming. Thus, a high oil level stands out as the most straightforward and common cause of oil foaming.