Hi volume oil pump vs standard volume pump

famous bob said

No argument here, but, liquid seeks its own level, if no air can escape the oil pump on a setting engine, the oil could not drain or come up the tube . Such is the reason my single line pick up, that has an upward loop down ( because of header clearance) , to the pan fitting doesn`t drain out ----I`m thinking. The oil pressure comes up almost instantly when I start it. ?????????????????

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'I can't visualize that but I'll take your word for the loop. As an explanation, if you use a standard filter and the plug up in the block above the pump is in place, that will help keep oil in the system below the pressure sensing point, for at least overnight and maybe for some days, depending on how well the 'flapper' anti-drain back valve in the filter seals. That is the main system design feature to keep things primed. You can't prevent the oil draining out of the system much beyond that point, once it starts 'downhill' to the mains.