oil

The advice is plain and simple: never use them! There are many oil additives and so called engine treatments (often sarcastically referred to as snake oils) available on the market but they all share one thing in common: none of them was ever proven to be advantageous, actual tests found quite the contrary more than once. Manufacturers routinely claim that independent laboratories tested their products scientifically but they don't rush to disclose the names of those laboratories or the circumstances under which the tests were conducted.

The primary job of the oil you put into your engine is to stop the various metal surfaces from grinding together, causing rapid wear of the parts. At the same time it has to dissipate the heat generated from friction, to transfer part of the heat of combustion away, to hold the byproducts of the combustion in suspension, not allowing them to stick to the engine parts. The oil has to comply with all these requirements under significant pressure and a wide range of temperatures ranging from the chilled engine in a winter morning to the high temperatures in an operating engine.