I haven't posted here in a long time (deployed).
I used Tufoil for around seven years with great results.
Those results being improved gas mileage, quieter engine noise, smoother running engine, quicker throttle response, etc.
I spoke of these things last winter here, and was kicked in the teeth for several weeks about it.
I looked up what NASA had to say about PTFE. NASA found that PTFE had a tendency to build up in the tiniest of oil passages which would eventually block oil flow.
So I quit using Tufoil in my engines. I use only Amsoil 5W40 Euro formula.
I do use Tufoil in my gearboxes and differentials. Using a synthetic gear oil with Tufoil is like taking 500 lbs out of your trunk. Smooths out the shifter, too. The entire drivetrain becomes silky smooth.
I did experience one problem with Tufoil when I had installed it in my '02 Volvo XC-70. I lost power. The engine would rev right past the power band and into the red kicking on the rev limiter. I had trouble getting around on the freeways because of this phenomena. So I removed the oil with Tufoil and replaced it with Havoline petro with Auto Rx and cleaned it all out. Then I installed Amsoil 5W40 Euro with no additives and the car now runs strong as ----.