What might cause excessive crankcase pressure?

Excessive crankcase pressure usually results from the phenomenon known as blow-by, which occurs when combustion gases escape past the piston rings and into the crankcase. This situation often arises in engines that have worn or damaged piston rings, as these components are meant to create a seal that prevents gases from leaking into the lower engine compartments. When the seal is compromised, the pressure from combustion can build up in the crankcase, leading to excessive crankcase pressure.

In contrast, while piston ring wear can contribute to blow-by, it is the direct escape of these gases into the crankcase that specifically causes the excessive pressure. Oil viscosity and excessive engine temperature can influence engine performance, but they do not directly create the kind of blow-by that results in increased crankcase pressure. Thus, the most direct and relevant answer to the cause of excessive crankcase pressure is indeed attributed to cylinder blow-by.