Originally Posted by CT8
Originally Posted by ZeeOSix
Please explain why you think a filter bypass opens up until oil pressure is achieved. I just want to know why you think that.
The bypass valve operates by the pressure differential between the unfiltered side of the filter element and the filtered side. If the oil filter is empty or the oil passages are empty the bypass valve will remain open until the oil pressure stabilizes with oil pressure on both sides of the element the bypass will "close"
The part in red doesn't work that way. Delta-p across the filter is only caused by the flow and viscosity of the oil. The bypass valve doesn't operate on oil pressure in any way, and it doesn't care if the filter is empty or full.
If you have X flow at 1 PSI or the same X flow at 60 PSI, the delta-p across the filter media is going to be the same. The filter being either empty or full, the bypass valve is going to be closed at start-up unless you have very thick cold oil and rev the engine way above idle instantly after a cold start. Too much viscosity + too much flow = more delta-p and maybe an open bypass valve, regardless of the operating pressure or if the filter is empty or full.