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Message: [QUOTE="jimdawg185, post: 1169499, member: 757"] The short story is spool valves shear oil down at an exponential rate. 7.3's do shear more than a non HEUI would. But 6.0s are just really bad. Ive seen reports where they shear the oil more than 20% in the first 1000 miles. Bypass systems are complex and simple at the same time. First, they all filter the oil. The key is two part. One, how well does it filter. And how well is it designed to bleed off the OE oil system and not hurt the OE functions and still push enough oil through the bypass to actually do some good. Most OE oil filters only filter nominally to 20 microns at less than a beta 200 at 25 micron. What that basically means is that its a carnage filter. It filters out big particles. Bypass filters are usually 1-3 micron at a higher beta. Most that I have seen are regular spin on filters. And unless they are microglass, they don't have much of a higher beta than the OE filters do though. SO they are a step in the right direction. The next step would be a depth media filtration, which would approach beta 1000 and is the best you can get in the filtration world. Why is this important.... Clearance of the hydrodynamic film of your typical engine bearing is 1-4 microns. These are the particles that are going to do the most damage in the long run because they can actually fit in between the asperities and do damage. Larger particles can still do damage, but not as much as the ones that are to size... This is not just important in extended drains, but for the life of the engine in general. Where it comes into play for extended PM's is that it helps the oil get the particles out. The detergent and dispersant package int he oil itself is more important in extended drains. You need reserves of these things for the oil to live and do its job. If they deplete, then the oil is no longer good. Good detergents grab contaminates and place them in the filter by making the particle larger (by bonding to it) and stopping in the large filter pores. [/QUOTE]