Should you use oil additives in oil?
No, and here are many reasons why not:
Most oils already have their own additive package, and AMSOIL is no exception. AMSOIL already provides superior protection, and should you add one of these additives, the additive formula may not be compatible with the additive package in the AMSOIL (or any oil, for that matter), and end up causing more damage than protecting. Adding an additive will also void the warranty AMSOIL provides with their product. AMSOIL has many times said that if the additive worked, they would have been using it in their oil already.
What kind of additives are out there?
Additives are generally using one of three ingredients to "protect" your engine: Teflon (PTFE), sulfur or chlorine. Yes, the same chemical you use in your pool you are pouring into your engine.
Some of the PTFE formulas would be Slick 50, QMI, Greased Lightning, and Tuff Oil. Those containing chlorine include Dura Lube, and Prolong. Many of these companies have already been sued or had the Federal Trade Commission (FTC) come down on them.
The carrier base of these additives are made from either kerosene or mineral oil, and then the "miracle" additive. When chlorine remains within an engine for a long period of time, as in normal oil usage, it breaks down and forms hydrochloric acid. A sulfur additive will break down forming sulfuric acid. These acids now start to eat away the inside of the engine and pit it.
The Teflon based additives often advertise that they bond to the engine. In order for Teflon to bond to a surface, it needs to reach temperatures much higher than the operating temperature of your engine. Should your engine reach these temperatures, you no longer would need an additive to protect it. The Teflon can also build up like sludge within the engine, blocking pours and channels, preventing oil from reaching places, often then causing damage. These PTFE additives also have large enough particles that a good oil filter will take them out of your oil almost immediately getting rid of any supposed benefit soon after pouring it in. But if it doesn't, and a bit starts to build up, it will continue to build until the area is starved of lubrication. I've heard from several well known local mechanics mention engines that they had worked on that had bearings go bad, massive baked on sludge deposits, or other engine failures due to an additive.
At one point the U.S. Army looked into a PTFE additive to see if it would benefit their vehicles. They trial tested 10,000 vehicles and found no evidence of improved gas mileage or performance, as advertised, however, 5% of the test vehicles did encounter some sort of engine failure.
Also as these additives start to break down and mix with other engine by-products, the exhaust gases formed tend to rust your tailpipe.
In addition, used oil is often sent to plants that burn it. Should you dispose of your Prolong or Dura Lube "protected" oil in a proper recycling station, it will most likely end up at one of these plants. As the chlorine burns, it now is converted to chlorine gas, and pumped into the air from the plant smokestacks.
One of the mechanics that gave me this information has sent several samples of various additives and oils to the AMSOIL labs so that he could have a better understanding of what they consisted of. Two such tests I have copies of were on Slick 50 10W-30 Motor Oil, and X-1R. The results of the X-1R test made it back to that company, and they sent a rather entertaining letter back to the mechanic. X-1Rs claims to be NASA approved. In a sense they are telling the truth, one of their products has won an award from the Space Awareness Alliance, however, this product is a lubricant for the Shuttle Crawler called "Crawler Track Lubricant" and not the X-1R oil additive that gets promoted to the automotive public.
I also have copies of two faxes from Texaco regarding Dura Lube and Prolong. It seems AMSOIL is not the only company that has come to the same conclusion of suggesting to avoid adding oil additives.
The last company I heard was under observation from the FTC was zMAX a few years back for not being able to support their claims..
Also click on some of the links I have found on additive reviews, the Consumer Reports findings, and FTC charges. Do your own search at the FTC Web Site located at www.ftc.gov.