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Lubricant Additives a comprehensive guide

Lubricant additives are solid particles that are dissolved or suspended in the lubricants to enhance their functions. They are organic or inorganic compounds that constitute between 0.1 to 30 percent of the total volume of the lubricant. The quantity of additives required depends on the type of machine you are using and the function of the lubricant.


Additives are used to for three primary reasons

  • Enhancing the existing properties of base oil by adding antioxidants, anti-foam agents, corrosion inhibitors and demulsifying agents.
  • Suppressing undesirable properties of the base oil by using pour-point depressants and viscosity index (VI) improvers.
  • Adding new properties to the base oil, like metal deactivators, detergents, extreme pressure (EP) additives and tackiness agents.


Types of lubricant additives

Formulation of an additive is a complicated and expensive task. A proper mix of chemicals determines its type and its function; it differentiates turbine oil from hydraulic oil and gear oil from engine oil.


Some general types of additives are as follows:

  • Anti-oxidants – Oxygen in the air generally reacts with the weakest components of the base oil all the time and in all temperatures. This reaction is accelerated by the presence of water or by high temperatures. This phenomenon is called oxidation and it creates acids that cause corrosion and sludge which causes surface deposits (Which results in increased viscosity). Anti-oxidants are used to enhance the life of the oil by delaying the onset of oxidation; they are consumed in the process of protecting the base oil and they are present in almost every grease and lubricating oil.


  • Rust and corrosion inhibitors – These additives create a chemical protective barrier that prevents the reaction with moisture and from metal surfaces, thus protecting the machinery from internal rust. Metal deactivators are also a type of corrosion inhibitors. Corrosion inhibitors specifically protect certain metals; hence a lubricant may contain several of them. These are also a common ingredient in most lubricants.


  • Viscosity Index Improvers – An increase in temperature of the machine causes the lubricant to thin out. Large polymer additives are added to retain the viscosity of the oil in such conditions; hence they are called Viscosity Index Improvers. They are extensively used in blending multi-grade engine oils. They are also used for lubrication in low temperatures for improving the fuel economy by reducing wear.

        There are certain drawbacks of using Viscosity improvers (VI) due to their size (High molecular weight). They are prone to be cut up or chopped by machine components. Gears and sharp edged components cause the most damage to Viscosity index improvers. Viscosity improvers are less susceptible to shear loss if they are of high-quality, it’s always better to get such additives from reputed brands like Castrol.


  • Anti-wear (AW) Agents – Anti-wear agents reduce the wear and loss of metal from a machine by attaching to its frictional metal surfaces. They are activated when two metal surfaces contact and react chemically to form a film that minimizes wear in the presence of heat. They also help in protecting the metal from corrosive acids. These agents get “used up” as they perform their function, after which the damage caused by adhesion will increase. They also help in countering oxidation. 

         All the chemicals that are used as Anti-wear agents are phosphorous-based, and the most common element that is added to it is zinc dialkyldithiophosphate (ZDDP). Some versions of ZDDP are intended for hydraulic applications and some for handling high-temperature lubricants. It also has anti-oxidant properties with corrosion-inhibition properties.


  • DetergentsDetergents are used to keep the hot metal components of the machine, clean (free of deposits) and to neutralize acids that form in the lubricant. They perform these two functions primarily in engine oils. They are basic or alkaline in nature; hence they become the basis of reserve alkalinity of engine oils. Originally, the detergents were barium based but now they typically contain a chemistry of magnesium and calcium.


This information is provided for guidance and informational purposes only. This website and information are not intended to provide investment, laboratory or manufacturing process advice.
The information contained herein has been compiled from sources deemed reliable and it is accurate to the best of our knowledge and belief. However, Castrol cannot guarantee its accuracy, completeness, and validity and cannot be held liable for any errors or omissions, as the results change depending on the working condition/environment. Changes are periodically made to this information and may be made at any time.
All information contained herein should be independently verified and confirmed.