I've never thought they were worth much. The old STP was only good for making your oil really thick so you would increase pressure and reduce leaks and consumption to some extent.
Today's engine oil already contains about as many anti-wear additives and detergents as you need. Alot of them contain zinc and molybdenum which work better than any teflon or silicone, etc. Also, additives can actually hurt the lubricating properties of your oil. Modern oils are engineered to be used by themselves. Additives can cause all kinds of problems like the moly separating out, foaming, and destruction of "clinging" ability to name a few.
Never add supplementary additives to quality engine oil
As a Fuels and Lubricants Engineer for a major oil company, I can categorically state to never add oil supplemental oil additives to your engine oil. Modern engine oil formulations are a complex set of base oils and additives that have been through a rigourous testing regime. The different additives within engine oil formulations have a chemical and performance effect on each other and the right balance is required for the oil to perform at its optimum. Supplemental additves can have a disastrous effect by upsetting this balance, and can result in additive drop out, oil thickening or diluting, and performance compromises. Often supplemental additives focus on one particular function, e.g. antiwear or viscosity, and this can be at the expense of another function such as anti-corrosion or dispersancy. Additionally, no oil manufacturer will warrant their product after it has been contaminted by supplemental oil additives. In summary, stick with the major and reputable engine oil manufacturers, adhere to oil drian intervals and alsways ensure the correct type of oil is used and you should never have an engine oil problem.
what austang said. i have tried a number of additives over the years, and i can tell you that they are, for the most part, a bandaid for an engine that needs rebuilding. i will say that lucas oil stabilizer is the best of the bunch, but i still wont use it in a healthy engine. i prefer a good synthetic oil like mobil 1 instead. there is however one oil additive i would consider using on an engine that has some miles on it, but is still a long way from rebuild time, and that is the BG line of oil additives. but they are kind of hard to find. best to use a top quality oil and save your money that you would otherwise spend on additives, and put that money towards say a gallon of gas
I have had good luck with non-Synthetic, so I was just looking to see if something could help out.
I don’t want to sun synthetic in my ride because it has been sitting for a long time and from what I understand Synthetics are more prone create leaks in a motor that has older seals.
I use a product called "General Motors engine oil supplement" or GM EOS when I break in a motor.At the GM dealer where I buy it they have told me that most of the mechanics there add it to their own personal cars every oil change.I have read on various sites that the level of zinc in todays motor oils is steadily decreasing and that it is important to have lots of zinc when you have a flat tappet cam.Some have even recommended that you run a diesel motor oil or racing motor oil if you have a flat tappet cam and that the newer oils with the SM rating are not the best for flat tappet cams.I am curious if the lubricants engineer,austang,would know more about this or if it is just internet tales.
Some have even recommended that you run a diesel motor oil or racing motor oil if you have a flat tappet cam and that the newer oils with the SM rating are not the best for flat tappet cams.
Thats partly why alot of 4-stroke dirtbike and some road bikers use Chevron Delo 400, Mobil Delvac, or Shell Rotella(or the synthetic versions thereof). They also have little or no moly, which will load up a wet clutch and cause it to slip. They purportedly have tougher base stocks than automotive oils.