Delvac 1 will safely hold 0.4% soot (not 4%). It meets all MB requirements. Soot holding capacity is a characteristic of the oil formulation, and Mobil 1 will not safely hold as much.
What happens is, I believe, that the soot particles become large enough to cause damage by abrasion of engine parts above the maximum rating. If you are using mineral base oils rather than synthetic, 0.2$ is probably the upper limit due to the poorer ability of mineral based oil to suspend soot. Changing at 0.3% is a safe bet. What kind of milage between changes are you getting? Peter
