Originally Posted by Will_w202

I was running "regular" Mobil 1 (10w40?) in a Jetta TDI a few years back, and switched to Mobil Delvac 1 (synthetic, not 1300) because I had heard it had great detergents. I ran the D1 5k before changing it, and my soot level was in the neighborhood of 8% - unacceptably high. That tells me the Delvac 1 cleaned the hell out of my diesel engine, and that the standard M1 wasn't cut ou for diesel use. I'd say 5w40 Delvac 1 is a safe grade to run for maybe 1000-3000 miles, just for cleaning, then switch to the M1 0w40.