The bypass valve reacts to the pressure difference between input and output of the filter.
Lower ratings are safer in maintaining oil flow, if the media is clogged or during cold start with thicker oil viscosity grades.
Remember bypassing oil filters means dirty oil gets in between the bearings and journals.
A high efficiency quality filter like Napa gold doesn't really require a bypass valve.
But that is just what works for me and how I use and maintain my lubing system.
Most folks prefer the added safety of a bypass valve.
