Most change the viscosity of the engine oil. Some also provide a coating of sorts to the engine internals and others help break up and flush out sludge. There are even some that serve as additives ...

“Many years ago, engine manufacturers recommended a break-in oil, which allowed the engine parts to accelerate a wear pattern break-in condition before switching to a conventional engine oi ...

I must admit I had never heard the concept before. I remember the days when you bought a new car and would break-in oil in ...