I know some things about oil. I know that before start up most of it is in the crankcase, a big metal container-y thing in the middle of my engine. There's a filler neck on the crankcase, capped by the top of the dipstick, and I know which line on the dipstick the oil level should reach. I know how to add more. I'm even certified to do so, because that's considered "elementary work" by Transport Canada. I'm awesome at pouring oil straight from the bottle into the crankcase without spilling any, if the wind isn't blowing. I know that if the wind is blowing, or a helicopter taxies by and I spill oil on the engine it makes a mess, and then the maintenance folk can't tell if the engine is leaking or the pilot is just an idiot. I know how to make a funnel out of an old oil bottle so that I don't make a mess. I haven't yet figured out how to get the oil stain out of my wool sweater from the time I knocked over the funnel, but it just looks like a shadow, anyway. I'm pretty good at estimating how much oil is on the floor, cowling and or belly, if there is a leak. And it doesn't take any special skill beyond resignation to a task to clean oil off the airplane's cowls and belly. When it's time to change it, I can drain the oil from the engine into a bucket without burning myself.
The four functions of oil we learned as student pilots: cleaning, sealing, lubricating and cooling. Thus I know the oil lets the moving parts slide instead of scrape against one another to reduce wear and wasted power; it fills in little gaps around the pistons in the cylinders so the pressure doesn't escape; it exchanges heat between the hot engine and the cold air that blasts in around the oil cooler at 20,000' and 170 kts; and it carries bits of carbon and dirt and whatever with it out of the moving parts and into the oil filter. I can specify the maximum and minimum pressures acceptable oil pressures on the gauge and I even know there's a skinny little line that runs to each cockpit oil pressure gauge along the leading edge of the wings from each engine. It seems too blink-inducingly simple to be the way oil pressure monitoring would work, kind of like using a transparent gas tank for a fuel gauge or a little porthole in the floor to verify gear extension, but I've used such systems, too.
I've always been impressed that the very same oil is also used to control the pitch of my constant speed propellers. A pump steps up the pressure three- to fivefold in order to drive the propeller to fine pitch, and I love those little diagrams of pilot valves opening and closing for on-speed, underspeed and overspeed conditions. (The one on page 72 of this Hartzell manual is, however, astonishingly terrible. You can't even see the way the valve operates. Don't bother looking at it).
So what's my confusion about oil?
It has all these really specific jobs to do and is vitally important to the function of the engine, but after it goes through the pump and filter, it just gets jammed into all the things its supposed to lubricate, and squishes out in a not very orderly fashion. It's supposed to leak in and out of everything, and I'm really not sure how it gets collected back to the sump after its adventures in the engine. Is there a complicated system of check valves and return lines in the oil scavenging system? I know the system used in the Beaver, where the oil just splashes up and drips back down is less advanced than the one in my airplane, but I really don't know how it works. Maybe there are elves. And if so are they the arrogant, bow-wielding kind from The Hobbit or the bumbling ones with oversized hats from Rise of the Guardians. It's probably more complicated than that, because I've watched them cut open the used oil filters and I've never seen any arrows or hats in there.
Also, the FAA mandated this:
INSTALLATION OF A PLACARD ON THE INSTRUMENT PANEL TO PREVENT FAILURE OF THE ENGINE CRANK SHAFT
I hope there's more than a dashboard placard preventing failure of my crankshafts.