Engine Oil Additives – Buy It or Know It?

Engine oil additives are substances that are soluble in oil. They are added to improve the engine oil’s performance as they alter its chemical or physical properties. Every manufacturer uses additives, however these additives should not be confused with those “miracle-substances” that are often available in certain supply stores.

Should I buy engine oil additives?

There are plenty of additives available on the free market, though they are very different from the oil additives that are used by the manufacturers. The additives used in packaged engine oil, whether in mineral or synthetic oil, are generally well coordinated with the respective type of oil (see below). This is very different when it comes to aftermarket oil additives: there is no certainty how the additives might interact with the different sorts of oil. If the worst comes to the worst, using an additive could result in an engine breakdown.

Engine oil additivesAutomobile manufactures generally advise to go without aftermarket oil additives. They also point out that when using those substances, warranty claims could become invalid. It is not forbidden to use them, however, in case of damage it will be checked whether the added substance caused the damage. If this is the case, the manufacturer assumes no liability and the repair costs have to be payed out of one’s own pocket.

Most common additives in engine oils:


Oxidation is a big problem for many materials. Engine oils oxidize, too, especially at high temperatures and when exposed to oxygen. Oxidation catalysts (substances that speed up the reaction) are for example metal residues and acidic substances that arise during combustion. When adding antioxidants to the engine oil, its durability can be considerably prolonged. Nevertheless, the oxidation cannot be stopped. Antioxidants are generally composed of: radical interceptors, peroxide decomposers and passivators.

Viscosity modifiers

The viscosity index (VI) describes the viscosity of the engine oil at different temperatures. That means, whether the oil behaves similar, both during summer and winter or whether it for example has the tendency to become thinner during summertime. Viscosity modifiers are usually polymers, which increase with rising temperatures and therefore allow the oil to operate at higher temperatures, while keeping its viscosity. They do not “thicken” the engine oil, as often believed, but rather prevent low viscosity at high temperature. This is especially important for multigrade oils. However, additives that increase the viscosity index of an oil eminently, lose their positive features extremely fast when heavily used. That’s why multigrade oils, which have to survive all kinds of different conditions, will age faster.

Antiwear additives

Metal-to-metal contact provokes often high material wear. Antiwear additives (as for example sulfur) prevent direct contact of the metals by building up a protective film that surrounds the metal parts. This protection layer is generally solid but is lubricated at elevated temperatures (running engine) and increased pressure, thus inhibits excessive material wear. This wear protection is especially important in the winter and during engine start.

Friction modifiers

Friction modifiers, as the name implies, reduce the friction forces between moving parts. Friction modifiers operate when it comes to mixed friction, that is the transition of dry (metal-metal) and lubricated (metal-oil-metal) friction. Mixed friction appears when the motor is set in motion. Friction modifiers form monolayers that prevent direct contact of the moving parts and therefore reduce friction.

Corrosion inhibitors

Corrosion describes the interaction (chemically or electrochemically) of a substance with its surroundings. The most common type of corrosion is the oxidation of metal, or, in other words, rust. Corrosion inhibitors try to prevent that by covering the metal in a protective layer, which inhibits the contact of the corrosive substance with the metal.

Anti-foam agents

Foam in engine oil prevents the motor oil from forming a lubricating film on the metal parts. That’s why manufacturers try to prevent the production of foam in engine oil by using anti-foam agents, typically silicone. With anti-foam agents, less air and gases are enclosed within the oil. Gases that are present in the oil can also exhaust faster.

Pour point depressants

The lowest temperature at which a liquid will flow is called the pour point. The liquid will solidify below this temperature- engine oil “thickens”. Paraffins, present in the engine oil, are responsible for this. They crystallize at low temperatures. Pour point depressants can lower the pour point so that the oil can remain fluid.


To keep contaminants from accumulating and agglomerating, detergents are used to “enfold” dirt. There are different ways to do that. The so-called peptization encloses solid dirt particles as for example soot or engine sludge, while the word solubilization is used to describe the process of binding liquid contaminants in the oil.


Detergents are similar to dispersants as they are supposed to keep the engine “clean”. They inhibit the production of residue at constructional elements, which are exposed to high temperatures. In addition, detergents are meant to neutralize acidic substances that emerge during combustion.


Photo by andrew jay

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