under hood

Sounds like it's time to have a compression check done to see if the rings are bad, the car is obviously consuming oil through the engine. Most commonly this is caused by worn piston rings, a stuck or clogged pcv valve, or worn/damaged valve seals... or if it is a turbo car, turbine oil seal failure. If the car smokes blueish smoke, it is most likely a piston ring failure, or something in the valvetrain. It's most likely time for a serious overhaul. Hope this helps!