I think the science is starting to get a tad clearer.
I have mine blocked,with a tiny hole drilled in it. Without a bleed hole , sometimes after an oil change,it would loose prime,no psi untill I would loosen the filter and bleed it.
Nahhh I guess the bypass won't hydro lock as oil that bypassed could travel on through the standard path and its not sealed at the end. I momentarily thought the bypass might be backed into sorta a corner above the cup with hole in it and it might cold hydrolock sort of.
But what about this.......
The oil pump is a gear pump positive displacement right. As like most pumps Its great at pushing but not so great at pulling. I was reading about a different gear pump that could self-prime 20 ft of a water column (~ 8.6 psi). But it doesn't say how long it takes to establish flow or what the cause and effect of exit pressure. Biggie here how long it might take to establish flow which would depend of pipe sizing and any leakage! It said it helps to have the gears wet. Thinking when I have worked occasionally with sump pumps and sometimes they prime fast other times not; air leaks are killer.
I think the oil pump should act similarly. It can push upwards of ~90 psi but might not be able to suck more than ? ~12psi?. Then think of conservation of flow it might only have ~ 12-14 psi ? of pressure to push (as it might not have much slippage wet and flowing oil but air? I would assume it isn't as airtight like a vane pump at priming because it hasn't picked up the oil flow yet. It sorta sits there and cavitates because the oil ahead of pump hasn't moved.
Because you want to establish flow quickly and get oil to the bearings you need a very small weep/prime hole to allow maybe a path of small resistance so it can bleed off this air pressure priming force and so the pump can pick up oil and build enough oil flow and thus oil pressure to exercise the bypass valves if the oil viscosity it requires due to temperature and flow resistance.
Don't hold me to the exact numbers above the bypass differential for the oil cooler might be ~20 psi and the oil pump can't build that priming especially with the head pressure required to get oil moving through the whole path in front of the pump.
The weep hole would mainly be for oil changes or because the drain-back valves are not airtight or fail so the oil pump pickup tube and gears get a small enough air pocket sometimes that might cause excessive priming time.
