I put Prolong in my truck a couple of years ago. While driving up the freeway doing about 65, the oil pressure went to 0. Since I didn't hear any unusual noises, I just drove home. When I got home, I smelled oil burning and saw smoke. I looked underneath the truck and oil was dripping from pretty much everywhere. It turns out something hit the oil filter punching a little hole in it.
I drove about 9 miles with basically no oil in the motor, no noise whatsoever and without any rise in engine temp.