Does anyone know why Continental designed the O-470 with a 12 quart sump and the IO-550 with an 8 quart sump?

When the 0-470 was developed in the late 1940's for the L-19 there was a military requirement that the engine at full power was to have enough oil to run until tanks empty . The L19 was rated to go full power for 6 hours and still have oil . The civilian 0-470 adopted the same sump -so 12 quarts .If you run over 65-70 percent expect to blow out (breather tube) down to about 9 quarts. I get 10-14 hours before I have to add a quart to engine .I only fill sump at oil change with 8 regular oil (Aeroshell 100 or Phillips 20-50 ) and 1 quart of Marvel Mystery oil. Keeps the belly clean and provides enough oil for safe operation. Not sure why 550 is 8 quarts ??

Years ago with my first partnered airplane, a 1970 Skylane, soon after we bought it, I thought to save money by changing the oil myself. Trouble was, I hadn't learned the proper way to safety-wire the filter, and I actually did it backwards. So start-up and running on the ground was fine, but then I took it for a short flight around the pattern, taxied back in, and when I got out of the airplane, oil was pouring out of the lower cowling because the filter had come loose. Right away, I found the problem and tightened the oil filter, then asked the local mechanic to help me understand the proper way to safety wire the filter.

Of course I was concerned because the dipstick showed that the engine had lost the top 4+ quarts and was down below 8, the minimum that the manual said it was supposed to have. The mechanic assured me that I hadn't done any damage, that the engine was actually designed to operate safely down with even less than 6 quarts in it. So of course I asked why it held so much, and his explanation was the same--that it's original design was so that it could be run flat out until the tanks went dry and still have enough oil to lube the engine.

Of course, as I became more experienced with the Skylane, I soon learned never to fill it with 12, and only fill it to 10 for a long cross-country. The longest cross-country we typically ran back then was from Laramie to Painesville, OH, about 9 hours of flying time with 2 stops along the way, first at either North Platte or Grand Island, and the second at Moline, IL. Starting with 10 quarts, I could count on adding a quart at Moline, which was at the 5 1/2 to 6 hour mark, as it would be below 9. Before leaving to return home, I'd add a quart at Painesville and again at Grand Island.

Later when I was doing SE charters, principally in Skylanes, if it was to be a long flight, the oil often had been topped off by someone before I got out there, and I could count on the top 2 to blow out by the time of my first fuel stop--just wasted. If I got out there and found the oil at around the 9 or 10 level, I just left it and took a quart with me. As often as not, I didn't have to use that quart at all.

Cary

I am running an O-470R that has about 75 since overhaul. I have been filling it with 12 quarts of Aeroshell 100 and it is still half past 11 after 25 hours of operation. I read somewhere that very low oil consumption can be indicative of problems as well. I'm not concerned, just adding more fuel for the money that I'm saving on oil. With the relationship of the oil intake screen to the bottom of the pan, I would expect that the thing would run down to about three quarts in level attitude. The O-470 is a very well designed engine, as is the IO-550.