I change oil for a friend in his '93 Nissan Altima (90K total miles on it) from time to time. Based on what I've read in this forum, we put a Wix 51361 on and filled with Pennzoil High Mileage 10W-30 (on sale $1.79 at Wal-Mart) last weekend. He drives almost 100% city, probably no more than 400-500 miles a month. I think his owner's manual says 7,500 miles between changes, but that would be well over a year away. Realistically, how long before I should start reminding (nagging) him to change it again?