I use it religiously, fixes MANY problems, especially on high mileage cars. I usually feed it through the brake boster or PCV vaccum line. But it can be added to a full gas tank or poured in the crank case too. Try and use it right before an oil change, so all the debries freed by the product will be taken away. And as mentionned before, seriously, use it outside, major fumes warning if used as recomended.