Jet engine oil is a one-way trip, as it's consumed like the oil in a 2-cycle. The oil consumption is slow, but it never returns to the reservior. It leaks out into the air/fuel stream, and is consumed in the burner section.
There's nothing wrong with lubricating an engine with vegetable oil with a bunch of additives. At least we don't have to dig it up from way underground, just plant a crop and process it appropriately.
Jerry
