If you put in too much oil, it reaches the cam and valves and will foam. When this happens, you lose viscosity and the smoke would more likely be due to some damage caused by an under-lubricated engine. Let's hope that's not it. There should be no "old oil" burning. Again, the oil should not be entering the combustion chamber. Well, actually, some very tiny molecular amount of oil does enter the combustion chamber as the piston rings float across the layer on the cylinder walls, but this is such a minuscule amount, it doesn't cause smoke or even a noticeable amount of oil loss between 12K mile changes.