My mental image of what happens on draining the oil, and removing the filer, goes something like this:
With the engine hot, to ease the draining of the oil, the oil flows out of the sump, oil pump (when the filter is removed), and oilways.
On fitting the (empty) oil filter, and refilling the engine with oil, the oil pump has to prime itself, fill the filter up, and pressurise the oilways sufficiently for the oil pressure warning lamp to go out.
There is no possibility of prefilling the filter on the FIRE engine as the filter is horizontal: the holes on "top" are on the sides when fitted to the engine.
Obviously at cranking speed <200 rpm it will take a while to fill the filter etc, but the load on the bearing journals is just the compression of the engine, and there's a bit of oil coating the surfaces which wouldn't drain out anyway.
My argument for doing it that way is that if you just start the engine - the light will go out fast(er), as the tick-over speed is about 900 rpm, but during that second or two the bearings are dry, and have the full load of the engine firing on them.
I'm not sure careful pouring will make any difference to the air in the system, as it mostly drains back to the sump, and is force fed to the bearings of the parts with heavy loads: crankshaft, camshaft, big ends, and anything else I've forgotten:I
It's not like the cooling system in the respect of airlocks etc, there's a lot of empty space which the crankshaft and conrods whiz about in, with a large puddle of oil - the sump - (with a wet sump system) underneath them.
It probably won't make a beans worth of difference anyway - I've heard enough things in the past which would clatter on start-up as all the oil had drained out of the bearings the night before, and they went for years without any problems.
It just niggles me a bit, that's all
