I'm not sure how a ceratek or stp oil additive make a car run smoother, unless you got a very carboned up combustion chamber. I used to be a big believer of thicker oil always being better, I've only changed that to a lower number in cold weather, such as going from 10w 30 to 5W30 for winter, for all my cars if I could find a good diesel 5w50 oil I would use that.
Synthetic oil is made the way it's supposed to be, great stuff. The problem people get into and not realize, a lot of mineral oils are filtered to very high standards and they are allowed to be called synthetic. Yes you literally have mineral oils rated to be synthetic when they are not. The other thing people don't know about mineral oil is that the first number is always the base oil. The second number is what all the additives do, thick enough when the oil gets hot. What happens over a long time is cams and gears and stuff cheer up the oil and those polymer additives get broken up and slowly the oil reverts back to what the base number was and no longer offers protection. This is why straight great oils are preferably in airplane use and extreme duty vehicles, you never have to worry about it breaking down
Synthetic oil is made the way it's supposed to be, great stuff. The problem people get into and not realize, a lot of mineral oils are filtered to very high standards and they are allowed to be called synthetic. Yes you literally have mineral oils rated to be synthetic when they are not. The other thing people don't know about mineral oil is that the first number is always the base oil. The second number is what all the additives do, thick enough when the oil gets hot. What happens over a long time is cams and gears and stuff cheer up the oil and those polymer additives get broken up and slowly the oil reverts back to what the base number was and no longer offers protection. This is why straight great oils are preferably in airplane use and extreme duty vehicles, you never have to worry about it breaking down