I have a 1999 Ford F-350 4X4 with a 7.3L twin turbo-diesel that I use to pull a 32 foot low-boy trailer. The truck has 109,000 miles on it. I decided to start using Prolong after a friend turned me on to it. Within ten minutes of using the product the engine noise decreased noticeably and acceleration was slightly better (this is saying a lot considering its a diesel engine). After an hour of use the diesel engine was as quiet as a gasoline engine and exhibited lower coolant temps as well as no valvetrain noise what-so-ever. I haven't driven the truck without oil to prove Prolong's ability to keep an engine from seizing up, and I hope I don't have to. But this stuff really does seem to reduce the engine friction, noise, and temperature. I'm now a life-long customer. Recommend it to your friends; they'll thank you later.
