The point raised earlier about stable oil consumption is a very important one.
I made the assumption that the oil consumption in the O 200 engine mentioned in the original post, was steady at the 1lt/hr. If it is a sudden new development than I would say you almost certainly have a sick engine. I had an engine failure in a fully loaded PA31 shortly after takeoff. I was faced with the choice of flying single engine, 100 nm over high mountains, or return to my departure airport which would require a NDB approach to minimums with a circle to land
. This was obviously not a great day for me. The moral of the story was the previous pilot suddenly had to put a total of 6 litres of oil into the engine in the last 4 hrs.
He did not think this developement was worth reporting to maintainance
Nevertheless I still think this level of oil consumption for such a small engine is not acceptable. If it is leaking this amount of oil than the belly is going to be literally dripping with oil/and or there will be 3 foot wide puddle under the nose. If it is burning the oil than it is either;
1) totally worn out: this is likely if it has a high time since overall and the low oil pressure is an indications that the bearing s are so worn that the clearances have increased to the point where the oil pump can not pump hard enough to maintain pressure. Heavily oil fouled spark plugs will also frequently indicate heavily worn/corroded cylinders
2) has a faling major internal engine component: symptons here are often a sudden dramatic rise in oil consumption, sudden increase in oil temp, new and unusual vibrations, and/or failure to make full static RPM at the beginning of the takeoff run.