That's it, and since there isn't any proof more, well what else to say. My last change on the Toyota Prius was at 5K, using Mobil 1 0w-30 and a Japan Denso filter. The driving was probably 90% short trip in town. In the bottom of the filter can was a thin layer of black soot like stuff. Never saw that before. I wiped it and the paper towel was black. So from that I gather the filter is very efficient, the dome end bypass didn't open and flush the soot, frequent cold starting even in CA with a Prius causes more soot than I expected, and I am content I changed early and "wasted" more filter and oil. I wouldn't have a way of knowing when the filter started to clog and the soot may be pushed through if I left the filter on. The element was black and the oil was dark red coming out and black in the recycling jug. The oil on the stick still looked golden and was exactly on full. To each his own I guess, according to what they see and the conditions. I'm continuing the one filter each change using premium filters.
