I love Seafoam.
My first experience was with a Tahoe with 250K on it and a lifter that would not stop ticking. Three treatments through the oil and that puppy was purring like its old self.
When I got the Formula it was running a bit rough. I Seafoamed the gas, vac and oil. When vac - ing it be ready for the smoke and do not go out on the road!
The gas tank treatment is easy and I do it at least once a year in all my vehicles.
Like mentioned above, I like to use it in the oil when an oil change is looming. And when its in there, you might want to take it easy on the engine.
Back to the Formula - after putting it in, I blew blue smoke on start up for a few days but for about 10 days I blew carbon deposits out the tailpipes.
It all cleared out and the car runs smooth and feels responsive again at 140k miles. SeaFoam! (I use it on the lawn mower, leaf blower, snow blower - anything with a motor - makes a nice fuel stabilizer too).