I think the dual filter is for looks.
Most of us change our
oil and filter once a year or 3000 miles.
Have you cut open a filter to see what trash is inside?
After the second change your
oil should be clean of all the engine building goop / trash. I change
oil and filter after 30 minutes and again after 50 miles. Then once a year in the spring in my Cobra.
Most filters bypass at 15 psi or less, so most of the oil is not filter every time is passes thru the filter.
The Motorcraft FL1HP bypass is set at 30 psi. Has a heavier metal case than other production filters. Good filter for $13.
I can't find the link to oil filter site. But here are a couple on oil. Oil filter is a world of it's own.
And oil, I think you need to be a engineer just to understand part of it. But it's fun to read when there is nothing on TV.
If you want the real story look at your bearing wear. If there are a lot of scratches then you have trash in your oil.
Dwight
Used Oil Analysis - Bob is the Oil Guy - Bob is the Oil Guy
http://www.animegame.com/cars/Oil%20Tests.pdf