My experience with snake oil is this.. seafoam does very little and is what I consider a extra gentle cleaner, I wouldent waste it adding it to engine oil or the gas tank I only use it for inductions on well kept up engines before a tune up. Marvells mystery oil is what I consider a medium strength cleaner, I add it to the oil system a few hundred miles before changing it. If I know a engine is carboned up inside I will use it for a induction service esp on a ford 3v...it softens the carbon and breaks it down to mush, cleans piston crowns, rings, valve faces and can free up lifters...run the engine 30 min then change the oil! lucas or berryman added to the fuel tank at fill up to clean the injectors..a quart of 90% iso alcohol if you think you have (up to 10 gallons) of water saturated fuel.
Running 2 cycle oil in a 4 cycle automobile all the time I would get worried about gumming up valves/seats, plugging or carboning up 3 piece oil rings and oil return ports in the piston ring lands, carbon build up on exhaust valves, cat damage, 02 sensor damage, charcoal canister damage, and carbon build up on the plugs. If it separates or falls out of suspension it could clog fuel filters, injectors and foul plugs causing a no start. A non fuel injected air cooled small engine could possibly benefit