Originally Posted by barry123400

Have him try running the car with the oil halfway between the measuring marks. There has been some discussion of filling oil to the top mark seems to make consumption increase . Thats until the oil level lowers down a quart or so. Also make sure he has the right dipstick for his model .They are color coded I believe. Also try to find out how much oil he is putting in during an oil change. Does it match the manufactures figures?

The diesels do not seem to reach a quart a hundred from old valve seals.The exceptiom might be if someone did a valve job and left the rubbers off. If the engine has any external indication of oil leakage it might increase to noticeable amounts at speed. A quart a hundred is a lot on those engines.