Since joining this forum I've become a recent convert to the advantages of synthetic oil in the motor. My question is - are there any concerns with switching from standard dino oil to a synthetic like Mobil One with a lot of miles already on the car? I've got a variety of vehicles (2 Fords, Volvo, Hyundai) with anywhere from 35,000 to 130,000 miles on them. I'd really like to keep them running in top shape as long as possible and I know a good, quality oil is a great first step along with routine maintenance. My local Autozone is offering 5 quarts of Mobil One Synthetic and an oil filter for $30 so I figure this would be a great time to get all my motors switched over. Thanks for your input!