I bought this car new, going by the maintenance minder I change the oil when it gets to 15%. It is always low when I do change it. Last week my wife got home and it was chattering. Shut it off and I checked the oil and put a quart in it. Never been that low. The mm was at 40%. I went ahead and changed the oil and filter yesterday. I use 0 w 20, that is what I have always used and what it calls for. I have read that some people go to 5 w 30. I do not know where the oil is going, its not leaking and burning it that I can tell. Car has around 131000 on it. Any ideas?