Be, It's my guess that the the rings are starting to wear. A compression check during the next scheduled oil change service should reveal any serious problems related to the rings. You may also want to have a tune-up in case the valves, timing, etc need to be adjusted. If you have a oil change and the oil becomes black within two weeks--that could be a sign of a bad head gasket. I advise you to check the oil about once a week in order to check the level and the color of the oil. Keep a record of the results. Jason