SuffolkD at aol.com wrote: Dan: Provided your enginee isn't "sludged" its the detergents working in the enginee cleaning away. -Scott by BOSTON Scott, it's not - at least I don't believe so looking inside the oil cap. Very clean in there... And I have always done my oil changes using M1 0w-40 and OEM filter at 5k intervals. Thx, Dan D '04 A4 1.8Tq MT-6 Central NJ USA