For those who have been reading our previous blog entries, the lubricating oil formula should already be a familiar concept. Lubricants are composed of base oil — available in mineral, semi-synthetic, and synthetic varieties — along with sophisticated additive packages.
These additive packages consist of organic or inorganic chemical substances introduced into the base stock to enhance its performance or introduce new, beneficial properties. Put simply, additives reinforce the characteristics of the base stock, raising its overall performance, reliability, and quality.
What exactly do additives do within a lubricant? What categories exist? This definitive guide covers everything you need to know about lubricant additives.
Additives typically make up as much as 30% of the finished oil formula. The precise proportion varies based on several factors, including the operating environment, the machine type, and the lubricant's intended purpose.
Based on the role they fulfill within the lubricating oil formula, additives serve the following functions:
As lubricating oil technologies have continued to advance, additive formulations have evolved alongside them. A broad spectrum of sophisticated additives is now blended into base oils to amplify their properties, suppress unwanted characteristics, and introduce entirely new attributes.
When discussing additive roles, it is worth noting that their proportion in the oil volume depends on the oil type and application. Equally important is the fact that additive selection is frequently what distinguishes different lubricant categories from one another — engine oils, hydraulic oil, gear oil, and so forth.
As a result, there is no one-size-fits-all answer when it comes to choosing lubricant additives. They are extraordinarily costly, and engineering an optimal lubricant formulation by selecting and combining various additive types is a highly complex undertaking.
Every formula calls for specific agents, and many variables are considered during the selection process. Additives are chosen, for instance, based on their capacity to satisfy certain industry standards and fulfill particular functions. They must also blend seamlessly with the base oil and remain compatible with any other additives present.
You have likely already encountered some of the most widely known lubricant additives — rust inhibitors, antioxidants, and viscosity improvers, to name a few. The following breakdown is designed to help you appreciate the importance of various additives and the roles they play in lubricants.
Depending on their function, additives fall into three categories: surface-protective, performance-boosting, and lubricant-protective.
Let us examine each of these categories in detail.
True to their name, surface-protective additives are designed to safeguard the metal surfaces of engines. This group includes anti-wear agents, anti-corrosion additives, detergents, dispersants, and friction modifiers.
Lubricating systems are subject to several types of mechanical wear. Among these are adhesive wear, abrasive wear, pitting, and spalling.
This is where anti-wear agents prove their value. Their principal purpose is to shield loaded metal components from wear and tear. These are polar additives that bond to frictional metal surfaces and undergo chemical reactions during metal-to-metal contact. They are generally compounds based on phosphorus, with ZDDP being the most widely used and recognized. Various forms of ZDDP are employed in hydraulic oils, engine oils, and other applications. Beyond antiwear performance, ZDDP also delivers antioxidant and anti-rust benefits.
Antiwear agents are thermally activated, forming a protective film that curtails mechanical wear. They additionally help shield the base oil from oxidation and protect metal surfaces from corrosion.
Over time, antiwear additives break down, and once depleted, the likelihood of metal surface damage increases sharply.
Corrosion Inhibitors
Corrosion is a damaging transformation of a metal surface driven by chemical or electrochemical reactions between the metal and its environment. It causes the degradation and weakening of metal properties. It is important to understand that corrosion does not happen suddenly — it is a gradual process that threatens all non-noble, ferrous metals.
The function of rust and corrosion inhibitors, therefore, speaks for itself. These are chemical compounds that, once introduced into the lubricant, reduce or completely eliminate internal rust and corrosion. They accomplish this by neutralizing acids and establishing a protective barrier that prevents moisture from reaching the metal surface.
Their mechanisms of action include:
- Passivation — they coat the metal surface to block interaction between the metal component and water or air.
- Neutralization — corrosion inhibitors neutralize corrosive substances. Carboxylic acids, for example, bind to the surface and neutralize alkaline compounds.
Corrosion inhibitors are widely used across various industrial environments and serve as an essential component in nearly all lubricating oils. Anti-rust additives are also a critical ingredient in many over-the-counter workshop and service sprays and fluids.
Depending on the operating conditions and the demands of the equipment, various formulations can act as corrosion protection agents. One such example is Zinc dialkyl dithiophosphate (ZDDP), which is also recognized as one of the most potent anti-wear additives available.
Detergents may be alkaline or basic, and are frequently used alongside dispersants. They are metal compounds of calcium or magnesium, as well as phosphates and sulfonates. Barium-based detergents, once prevalent, are seldom used today.
These are multipurpose agents that fulfill several key protective functions. Among other things, they keep hot metal components clean and neutralize acids generated within the oil.
That said, these metal compounds can leave ash deposits when the oil combusts and may form undesirable residue at elevated temperatures. For this reason, many OEMs specify low-ash oils for equipment operating under extreme heat conditions.
Dispersants are commonly found in motor oils, where they help keep the engine clean and free of deposits. Their main purpose is to ensure that insoluble soot particles from diesel engines are dispersed or held in suspension within the lubricating oil.
Dispersants are generally paired with detergents to neutralize a greater volume of acidic compounds and keep contaminant particles suspended. They are typically organic and ashless, such as polymeric alkylthiophosphonates and alkylsuccinimides.
Friction modifiers are primarily used in engine oils and automatic transmission fluids (ATFs). Their core function is to modify the friction characteristics between engine and transmission components. In engines, they reduce friction to improve fuel economy, while in transmission systems they optimize clutch material engagement.
The primary role of this additive category is to enhance properties that are already present within the lubricating oil.
Pour Point Depressants
The pour point is the lowest temperature at which a lubricant remains in a fluid state. At reduced temperatures, wax crystals in mineral oils solidify, interrupting the oil's ability to flow freely.
Pour point depressants address this challenge directly. By reducing the size of wax crystals within the oil, they preserve the oil's flowability even at sub-zero temperatures.
Seal swell agents interact with elastomers and induce a slight expansion of elastomeric seals. They are generally formulated from organic phosphates.
Viscosity Index Improvers
The viscosity index is a standard method for quantifying how a fluid's viscosity changes in response to temperature fluctuations. A high VI indicates that the lubricant's viscosity remains relatively stable as temperature increases.
Viscosity index (VI) improvers are polymer-based additives that prevent a lubricant from thinning as operating temperatures rise. Also referred to as viscosity modifiers, they enhance the viscosity of the fluid. These additives are used in multigrade engine oils, gear oils, automatic transmission fluids, power-steering fluids, greases, and certain hydraulic fluids.
VI boosters also improve oil flow at low temperatures, reducing wear and enhancing fuel economy. They are likewise used to protect and lubricate high-viscosity hydraulic and gear oils, and to improve their cold-start performance. Several types of viscosity index improvers exist, with olefin copolymers being the most prevalent.
However, VI improvers do carry certain drawbacks. They are susceptible to mechanical shearing — certain engine or gearbox components, for instance, can fragment the large VI polymer molecules into smaller pieces, significantly diminishing their capacity to sustain lubricant viscosity.
This is precisely why the quality of VI improvers matters considerably. Higher-quality VI improvers exhibit greater resistance to permanent shear loss.
This category of additives works to diminish the negative properties of the base oil or reduce the changes that take place over the lubricant's service life.
Air ranks among the most serious threats to base oil integrity. Although oxidation occurs across all temperatures, it accelerates with rising heat and is further promoted by the presence of water, wear metals, and other contaminants.
Oxygen promotes the formation of acids that lead to corrosion. It also contributes to sludge buildup, which raises viscosity and causes surface deposits to form.
This is the domain of antioxidants, also known as oxidation inhibitors. They are among the most fundamental and critical additives, present in virtually every lubricant formula.
Their primary function is to extend the service life of the lubricating oil. Antioxidants are sacrificial additives — they are consumed during the process of oxidation protection and gradually degrade and disappear over time.
Metal deactivators represent another critically important additive class. These are organic substances containing nitrogen or sulfur, along with amines, sulfides, and phosphites. The central role of metal-deactivating agents is to stabilize the lubricant by deactivating metal ions — a task they accomplish by forming an inert protective film on the metal surface.
Anti-Foaming Additives
Anti-foaming agents, or foam inhibitors, are silicone polymers and organic copolymers that lower surface tension and prevent the lubricant from generating foam bubbles.
They can also indirectly reduce oxidation risk by limiting the contact area between the oil and ambient air. These additives are used in very low concentrations within oil formulas, as excessive amounts can have the opposite effect and actually encourage further bubbling.
As the examples above make clear, a vast array of chemical reactions is occurring continuously during the machinery lubrication process. Given this complexity, it comes as no surprise that the additives within a lubricating oil gradually lose effectiveness over time.
Additives are consumed and degrade through multiple mechanisms. Some simply decompose. Others are absorbed into metal, particle, or water surfaces. Still others are removed through filtration.
As a general principle, the longer a lubricant remains in service, the less effective its additive package becomes. The practical consequence is straightforward: the lubricant can no longer perform as designed. Additive degradation leads to increased viscosity, sludge formation, metal component corrosion, and accelerated equipment wear and tear.
Naturally, the durability of an additive package is tied to the quality of the lubrication solution in use. Inferior-quality oils will experience additive degradation far sooner. This is why it is always advisable to choose high-performing lubricants capable of lasting longer and delivering superior protection and performance for your machines or vehicles.
At Valvoline, we have been developing, refining, and delivering our lubrication solutions for over 150 years. Every product in our extensive lineup is manufactured using the highest-quality base oils and additives.
Whether you require engine oil, transmission fluid, hydraulic oil, a coolant, or any other professional fluid for industrial use, we are equipped to meet your needs. Leveraging the most advanced additives available, our products deliver extended service life along with the highest levels of protection, quality, and reliability.
Additives are a foundational element of any lubricating oil formula. They amplify the positive properties of lubricants while minimizing undesirable ones. Above all, they elevate the overall performance and reliability of base oil by introducing new characteristics. This is why selecting dependable lubricants built around high-quality additive packages is so essential.
Uncertain which lubricant is right for your application? Consider consulting our Lubricant Advisor or locating the nearest Valvoline distributor in your area.