Normally the only time the oil goes missing is if it can not drain back into the pan. Do not run it with the extra oil in there. Has the oil light come on?
Look in the oil filler cap hole to see if valvetrain looks clean or covered in sludge. Check the hose to the PCV valve. It's hard to get to without taking off the intake tube and MAF.
This engine has two PCV fresh air hoses so unless someone changed that the crankcase should not be under vacuum. Just to be sure run it with the oil cap off. Put you hand over the hole to see if there is any suction. There should not be.
If it takes several minutes for the oil to drain to the pan after the engine is shut off, the drain galleries may be blocked. The valve covers must be taken off to clean them.
