the really best easy way to determine when a filter will bypass is to simply ask the manufacturer. Generally I would think they are given quite a wide margin to allow for accumulation of contaminants, and the aforementioned cold starts. But you would need to install at least a gauge before and after the filter,
the best would be an actual differential pressure gauge, to determine what exactly is going on in YOUR filter. However without actually installing said gauge(s) This is purely speculation, on all of our parts. I have taken thousands of readings on probably a hundred different pieces of equipment with differential pressure gauges, most of them run around 3-8 psid. (We would change the filters at around 8, or what ever that particular piece of equipment specified) True they were large diesel engines for maritime use, steam/gas turbines, reduction gears, hydraulic systems, things of that nature (I have never seen an automotive engine with a differential pressure gauge) and yes I will concede it does vary with pump RPM. but not to the extent that it will exceed the bypass setting. Certainly not to the degree that you could say "at 4-5000 RPM." With any sort of authority. I have also watched the differential on way too many filters climb as time went on, to NOT use a filter. They are catching something, not anything you can see, but they are clogging up nonetheless. They never really approached the bypass setting, but did rise appreciably.
