The 3.9 when running properly is a smooth and very quiet engine ...that is one of the many reasons why I love this car...this friction modifier just brings it to a whole new level of smoothness ...after initially using this product and changing the oil for the first time I literally seen the oil bead up on my plastic oil pan catch it was like rain going over a fresh rainx windshield ...I can only imagine what the internals of this engine are doing with this oil running through its vains ...LESS FRICTION MEANS LONGER LIFE... I've never had a smoother engine in any car In my entire life after using this stuff...hats off to the German's who engineered this stuff...simply amazingWhat did it do, Dutch? Please do tell!