I have used Tufoil for a long time; with 1-5% PTFE by weight, I haven't experienced any issues. I started using it in the late 1980s due to the fact that in Omaha, the engine on my Honda Accord would make a loud noise on really cold days. After putting in Tufoil, the noise went away. In our Lexus RX330, the UOAs have come back with no concerns (just additional moly). I put 4 oz in at each oil change, change the oil every 5,000 miles and the filter (Fram Ultra or OEM) every 10,000 miles. Lexus makes such a bullet-proof engine, I would never say Tufoil is a miracle additive, but from my experience, it doesn't hurt. As always, YMMV.