Very potent engine flush in a can. Problem with an engine flushes is it loosens up and moves hard carbon that is sitting where it won't hurt anything and moves it to places where can then do damage(getting into main bearings and between camshafts and lifters, etc) and most attack engine seals causing leaks eventually. Engines do not have to be spotless inside to function well, do regular short oil change intervals with a quality engine oil and your engine will last longer. Additives tend to do more harm than good.
I use Wynn's as a motor flush. Pour it in and let the engine idle for 10-15 min then drain.I wouldn't leave it in . I just used 2 cans in our new ( used) JCB forklift ,when I changed the oil and filter.