While I do not believe in using oil additives as a general practice, MMO has its place. I had a neglected Chevy pickup with a 305 small block. I tried a couple 3000 mile runs with synthetic oil, it seemed to be doing some cleaning, but still had valve noise from clogged up hydraulic lifters. I dumped in 1 quart of MMO during the last 4-500 miles of an oil change , and the lifter noise was gone and never returned. The oil came out pitch black, so it was apparent some cleaning was happening. Not saying MMO is a miracle, but can work well as a mild cleaner in a dirty, neglected engine.