"The poster" I am referring to is you. In post #19, I stated: "Negative. I was responding to a comment in post number 11, where it was stated: "Only bad thing that could happen in that scenario is if the oil pump goes into pressure relief before the filter goes into bypass could cause some decrease oil flow to the engine oiling system"". I had set the premise that I was referring to your post (#11) in my statements.
I was essentially agreeing with both of your subjects: (1) The oil pump pressure relief valve is going to be way higher than any filter bypass valve setting, and (2) "if" the filter bypass valve happened to be higher than the pressure relief valve in the pump it could cause decreased oil flow to the engine.
I would take (2) a step further and suggest there could be NO oil flow to the engine if the pump relief was lower than the bypass setting. In this hypothetical situation, lets say the filter bypass is 22, and the oil pump relief is 20. This situation is presuming the filter media is so plugged up that it is creating a 22psi differential, AND/OR the oil is so thick, that it is creating a 22psi differential across the media. Upon startup, the pressure throughout the system is zero. The oil pump starts sending oil the the filter, which is not allowing any flow until the system pressure attempts to reach 22psi. The pump relief is opening at 20psi, not allowing the 22psi differential to be reached, and the engine starves for oil.
I was giving the lowest oil pump relief pressure I could think of (35-40psi), to note that in all probability the oil pump relief is higher than the filter bypass setting.
I would expect lower oil pump relief pressures to be developed (if they haven't been already) to reduce engine load and increase fuel economy. Post #22 suggests this has already happened. We know that a PD oil pump has to have a relief, because if it didn't, the pressure theoretically would be infinite if the oiling system could not pass the entire volume of the pump output. This would either stall the engine or break something (oil pump drive shaft, stripped gears, etc). A pump trying to pass oil through with 80-100psi of back pressure will pass all the volume with enough released to keep the maximum pressure at 80-100. The pump is still fighting against this pressure and using energy to do it.
My suggestion in post #13 is based on the assumption that tighter tolerances, or more accurately, tighter clearances would cause the pump to bypass more oil through the relief valve, thereby reducing flow. As the engine wears, less oil is relieved so more flow is achieved. This is the increased flow I was referring to. You suggest that the oil pump relief valve almost never opens, I disagree with that.
If you have a pressure gauge, and you know for a fact that the pump relief is set at 100, and your gauge never gets over 80, then I would agree the relief valve never opens. That would tell me the pump is delivering maximum flow to the engine under current condition. There is no reserve. As the engine wears, pressure will surely drop. Some put higher viscosity oil in to "boost" the pressure, this will accomplish that, but flow will suffer if that gauge hits 100 in our hypothetical situation here, suggesting oil is now being relieved and flow is dropping. In real life, most vehicles do not have oil gauges, they have a light or a DIC message saying low oil pressure. Most of the time, we are guessing and assuming. If you have a gauge, on a very cold startup you can probably assume the relief valve is open. That is your reference point for opening pressure. If the gauge is pegged, you still don't know, but you can assume that when that gauge starts to drop the valve is closed.
I think most oil pressure sending units are BEFORE the filter, so an increase in pressure may suggest increased resistance through the filter up until the bypass opens. Once again flow will be the same, as the restriction will cause more pressure to be needed to push through the media. This of course assumes the relief valve is remaining closed. All of this is variable, depending on viscosity due to temperature or actual oil viscosity. You would have to have the oil at the same temp and vis to use pressure changes as a guide to filter restriction, once again, guessing and assuming......