I would have to respectfully disagree with this statement. When buying a used, high mileage vehicle, you never know what kind of gas they were running or how they took care of it. I have bought several vehicles from auctions and always do the Sea Foam treatment, then run good gas from then on out. I once bought an old survey truck with 173k mi on it from my old company so I knew the maintenance records were up to date. It ran rough and sounded like it was missing so I did the sea foam treatment and it immediately smoothed right out. Ran that truck in my hot shot service and never missed a beat. Had an overhaul done at 500kmi. Mechanic complemented me on how clean the valves and fuel system was.But as AZ01TJ was wary of, why do you think you want to add Sea Foam? In my personal opinion, Sea Foam is little more than a very expensive form of snake oil. It claims to do a lot of jobs but is not all that good at any of them.