I am new to this site. I had been running between 50 and 90% filtered to less than 10 microns used oil picked up from auto shops and ran through my 3 stage filtration system. Have ran a truck a 7.3 mechanical injected ford turbo diesel with nearly 200,000 miles on this for approx. 20,000 miles with minimal trouble. Recently have been putting about 10% of this filtered oil in my girlfriends 97 tdi jetta. Have seen no change in how it runs. Has anyone experimented with used oil in TDI's? I am thinking about uping the % as the weather gets warmer.