What is the primary cause of excessive crankcase pressure?

Excessive crankcase pressure is primarily caused by cylinder blowby. This condition occurs when combustion gases escape past the piston rings into the crankcase during the power stroke, leading to an increase in pressure inside the crankcase. As these gases mix with the engine oil, they can create a foamy mixture which further exacerbates the pressure issue.

Cylinder blowby is indicative of worn or damaged piston rings or cylinder walls, which compromise the seal and allow combustion gases to bypass the combustion chamber. Addressing this issue typically requires inspecting and possibly overhauling engine components to restore proper sealing and functionality.

In contrast, factors like oil viscosity, fuel contamination, or high ambient temperature may contribute to engine performance issues or oil degradation but are not the primary drivers of increased crankcase pressure. Oil viscosity affects the flow and lubrication properties of the oil, but it does not directly cause blowby or crankcase pressure increases. Fuel contamination can lead to engine damage and misfires, while high ambient temperature can affect engine operation; however, they do not specifically relate to the mechanism of crankcase pressure buildup like blowby does.