i've been running the HP6 for a while now, when we've changed filters we always cut the old one open just so we've got something to look at while we're having a beer. the filtration media is huge, it has so much capacity for catching debris we only change filters twice a season. the by pass valve never looks like it's been open on any of our cut open filters. the seat although is set at 20 is rather hard to force open with your finger & in most cases feels like the first time it has opened when we push on it as it feels easier second time round. i'm sure if it does by pass we'd have seen a flucutation on the data logger since it reads after the filter & a blockage of the filter would be apparent when the engines hot at idle.