On a newer engine with today's modern oils I can't see myself adding any additives just yet. Waste of $$ IMO. Use to use STP back in the day but then again ALL of us did.
could be snake oil. but since our warranty is done and im changing oil on my own, i've tried it the past 2 changes. guess we shall see.
in-laws have several cars over 400,000 km that still run mint, although rotten from winters, and have always used it so i figured id try it out. long term test ahead!