engines hold 7-8 litres, over 1&1/2 gallons.if crankcase vent oil sepparator or diagphram breaks the oil can be sucked through air intake using lots of oil,part costs £40 uk 30 mins-1 hour fix,car should be ok if this is problem.same problem usually makes car run rough from cold start. you can test vaccum pressure if you take care working in proximityto cooling fan, start engine-then undo oil filler cap-slightly lift filler cap and if suction is strong then this confirms problem. proper testing uses light pressure vaccum gauge on oil filler.