according to a series of laboratory tests and real-world analysis, oil additives have the potential to do far more harm than good. Lake Speed Jr. spent 12 years as Joe Gibbs Racing's lubricant specialist, so if anyone knows how oil works, it's him.

Speed Jr. picked out nine oil additive products you can find on the shelves of any auto parts store for this test. Stuff like Marvel Mystery Oil, Lucas Stabilizer, Rislone ZDDP Supplement, and Seafoam oil treatment are all extremely popular, but according to this test, you're better off leaving them out of your engine's oil.

In an oxidation test, Speed Jr. discovers that both Lucas Stabilizer and Marvel Mystery Oil increase the viscosity of the oil and cause imbalances in the mixture, decreasing the oil's effectiveness. In a separate test, he discovers Seafoam pulls in water from the atmosphere (the presence of water in an engine is bad) and actually boils away before the engine reaches operating temperature.

Oil Extreme, another additive, is especially dangerous for direct-injection motors, Speed Jr. says. The high amounts of calcium and sodium present can actually cause low-speed pre-ignition, giving it the potential to cause serious damage. The Rislone supplement is also bad, Speed Jr. says, because it raises the acidity of the oil, opening up the engine to corrosion-based damage and excess bearing wear.

In short, Speed Jr. says you should stay away from oil additives and instead choose the correct base oil for your engine.

https://www.motor1.com/news/719617/oil-additives-test

I notice STP wasn't included.