I have used it on a Perkins marine engine. It had an immediate effect raising the oil pressure and lowering the running temperature. The one I used was Wynns Formula 1.
Some friends of mine who know much more than I do about engines say it does nothing but I can only judge by my own experience.
HI Bob, have just had an engine flush on mine to try and get rid of noisey tappets, after flush noise was a lot less but still there, so took a chance and put in some Wynns, the noise has gone,but i still listen for it every morning when i go to start it, keeping everything crossed.
I used Wynn's fuel injection cleaner on my 5 year old Polo the other day, and absolutely swear by it now! The car always used to stall every time u lifted off the gas, really annoying. Dealer couldn't fix it and this was a last resort before buying a new throttle body. Turned out i didn't need to! Power(!?) fully back to normal. Best fiver i spent in ages....