Bypass valves are a crutch to protect the element from getting smacked. The non-metalic elements don't flow well enough to handle a pressure spike. There are lots of theories about why some valves are set at different deltas than others, and why one engine somehow needs a different setting then another engine, but the oil pump never sees that valve, it just does it's job, no matter what the setting. Pete has the right idea, there's a lot more bypassing going on that we know about. It's part of the national, don't ask don't tell policy. The full flow fluffy oil filter idea is credited to Purolator in 1927. Cars and engines have changed a lot, filters, not so much. Just like the change to detergent oils and multigrade oils, someday we'll change to stainless steel elements and have a modern element. The only reason for not switching is that the land fills need more leaky old used oil filters. How the heck to you clean one so you can throw it away. With a stainless steel, washable element, you can ditch that bypass valve and stop your filter from washing already filtered gunk back into the engine. But, for these cheap under five buck filters, the land fills will not want for more cr@p to keep them full.