My mom-in-law's car needs 10,000 mi OCI. It is a 1998 Chevy Malibu, 3.1 V6. She drives 10k miles in 6 months (a lot of highway miles), so I want to minimize maintenance. In an nutshell: I have been changing her oil along with mine and my wife's, every 6 months. I was stunned to learn that her car was running funny and she checked the oil--it was 3 qts down. I then learned that she had 10,500 miles on the oil! Though I will check carefully for mechanical issues and overt oil-burning, I have a hunch that the oil simply broke down so severely that it ended up being burned, as I have not noticed any leaks, and her car has done well with 5-6k mi OCI's. So, I think I need a more robust oil. I simply don't have the time to change it more often. I was thinking about using a synthetic (Valvoline, Pennzoil Platinum, whatever)and a good filter (PureOne). Edit to add: the oil weight is 5w-30, and her current mileage is about 135k. How does this strategy sound? Are there any conventionals that can withstand this service interval? Would a heavier weight (HDEO) be advisable (we do have some cold winters here)?