Idk, I know people either love it or hate it, but I fall somewhere in the middle.. I always have 4+ bottles each of the liquid regular Seafoam and the DeepCreep spray. I do not use it religiously, and I am aware it is not a perfect product, but I have had some great success with it and I take comfort in knowing it is a petroleum product rather than solvents and such.
I use it for cleaning throttle bodies, from the.butterfly valve to down the neck, and I have yet to find anything that works better (some work just as well, but are more expensive and/or harder to find).
It does work well in an engine with known carbon buildup, especially if the engine has the brake booster and PCV lines on opposite ends of the manifold. I let the engine suck it in both at the same time, let it soak, and I have seen a significant reduction in carbon buildup. I have used it on cars that I know had zero or minute amounts of Carbon and there is very little smoke, while heavily carboned cars have put out a steady smokescreen for 10min or more!
It does a great job as an all in one FI cleaner and fuel preservative, both in 2 and 4 cycle engines. I have even used it to clean the carb throat on my at the time 5yr old Honda mower and it put out a ridiculous amount of smoke (I added less than 1oz total). Now, the mower starts first pull.everytime instead of 5-6 tries, does not stall under heavy load, and it is a good 10% quieter; best of all, gas consumption went down, as instead of having 10-15% of a tank left when finished, I now have 25-30%, and there is never any black/sooty exhaust.
I know it works in engine oil as well, but it is more of a 3rd-4th line product. If a good syn oil (RL-RP-PU-PP) is used for a while first, then MMO or equivalent is used, then I would go to Seafoam. I do not have experience w Kreen etc so I cannot say, but I do believe it is better to use SF before resorting to any engine flush (last line).
The theory being that you slowly soften the sludge/varnish/carbon, then slowly use more aggressive products to eat away at it, circulating dissolved particulates into oil filter, and no chunks.
But, just as with any other additive, people have their own opinions. I like Seafoam, and I have been trying MMO recently so.we shall see how that goes. Mostly, though, money spent on additives is better spent on the best oil (skip additive = afford Redline oil, amazing cleaner itself) and top tier gasoline.
Of course, everyone needs RL SI-1 and ChevTec, that goes without saying.
