I have a 2005 Chevy Classic with the 2.2L 4 cyl. This started at about 150000 miles. It doesn't need oil after a change for about 3000 miles. I normally change at 5K intervals. After it starts needing oil it goes progressively less before needing another qt. Last time I changed it at 4700 miles because it needed oil. It used 3 qts between 3k and 4700 after not needing any the first 3k. No noticeable leaks and dry underneath. Currently running Pennzoil HM 5w30. I've also tried Valvoline Maxlife. What causes this? Any advice is appreciated.