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Premium Member
2020 Onyx
19,580 Posts
There are other oil filters that specify a high bypass pressure, and sometimes the manufacturer provides a TSB explaining why. In the case of Subaru, our oil pumps are exceptionally high volume and they are positive displacement pumps, so the higher the RPM the more it will flow in a nearly linear relationship.

Someone else did a study of oi filter bypass using an electrical connection that would turn on a light whenever the bypass valve opened, but it was not on a Subaru - but the principles are the same. It did open at cold start or high RPM and as the filter gets used, over time the bypass filter opens for a longer period of time, since a used oil filter doesn't flow oil as well as a new one (the pores in the filtering media get partially blocked and pressure differential across the media increases).

(link is russian use Google Translate)

So I don't recommend the use of a low bypass pressure oil filter.

Here's a post about different manufacturers using high bypass: The magical/mystical 23.2psi oil filter bypass spec.
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