Tagged: viscosity

Effects of Using the Wrong Engine Oil

Sometimes, the wrong engine oil is used. Whether it’s an issue of the unavailability of the correct stock or trying to standardize across the fleet without consulting the manufacturer’s recommendations, numerous issues can arise when the wrong engine oil is used.

Engine Sludge Build-Up

One of the most common side effects of using the wrong oil is a build-up of engine sludge. If we recheck the API standards, oils were designed to reduce sludge formation. When the incorrect oil is used, it cannot adequately compensate for the engine’s conditions, simply because it wasn’t designed for that purpose.

This can also occur when oil is used with an incorrect viscosity or with the wrong fuel (specifically, the concentration of sulphur for diesel engines).

Increased Friction and Wear

Earlier, we discussed how OEMs typically recommend several different types of viscosity for engines, depending on the specific conditions. However, if a viscosity is used that is too low to provide the correct amount of support and separation between the two surfaces, then increased friction and wear can result, damaging the engine’s internals.

Poor Performance and Efficiency

With the incorrect engine oil, the engine will not perform at its expected efficiency. This will directly impact its overall performance. If the viscosity exceeds the recommended value, the engine must work harder to achieve the same results, resulting in poor performance and decreased efficiency. Similarly, if the viscosity is lower than the recommended value, increased friction will result, leading to higher heat and reduced engine efficiency.

Damage to Engine Components

As stated above, a viscosity that is either higher or lower than the recommended value can damage the equipment’s internal components. Similarly, if an incorrectly specified product is used, it may not withstand the engine’s regular environmental conditions and can break down prematurely, damaging its components.

Potential for Engine Failure

Using the incorrect oil, the engine’s components will not receive the necessary protection, whether it’s due to the incorrect viscosity or the wrong mix of additives. This can lead to premature oil degradation, which in turn may result in engine failure. The correct oil will be able to protect against these harmful conditions and keep the engine from failing due to lubricant-related issues.

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Automotive / Oil Properties / Strategic Tips

The Importance of Regular Engine Oil Changes

Some oil manufacturers claim that their oil, when added to your engine, will remain “golden” in color and not turn dark. Every engine produces soot /carbon as a byproduct, so if the oil does not change color, it means that the soot/carbon is likely remaining stuck on the insides of your engine, which can lead to engine failure.

In these cases, the oil, especially motor oil, contains detergent and dispersant additives that keep the soot or carbon suspended in the oil. This ensures that these deposits do not adhere to the engine’s internal components, causing clogging of smaller clearances and damaging the engine. Hence, an oil change removes these accumulated deposits. There are several other advantages to changing oil regularly for these engines.

The Importance of Regular Engine Oil Changes

Preventing Engine Wear and Tear

Motor oils are formulated with around 30% additives. These additives can perform various functions, including protecting the internal components from wear. However, over time, they become depleted and should be replenished. Changing your oil regularly can help with that. With an oil change, there is a replenishment of additives that protect the equipment.

Maintaining Proper Engine Functioning

Over time, the viscosity of the oil in engines will decrease due to the conditions that exist within the engine. There will come a time when it reaches the end of its life and will no longer be able to protect the engine. At this point, the crosshatch on the cylinder walls can begin to experience some polishing, as the oil can no longer provide the necessary protection. By changing the oil on time or regularly, this can be avoided, and the engine can maintain its proper functioning.

Avoiding Costly Repairs

When the oil starts to degrade, it loses all its protective elements, and wear can start to occur. With frequent oil changes, this can be avoided as new oil will be able to protect the engine and its components to the best of its ability. This way, increased wear can be minimized, and costly repairs can be avoided.

Following Manufacturer Recommendations

Manufacturers typically recommend oil changes every 5,000 to 7,000 kilometers for passenger cars; however, this interval can vary depending on driving habits, environmental conditions, and even the type of fuel used. Oils are designed to protect the engine, and when they reach the end of their life, they can no longer fully perform this function. By changing the oil regularly (or, in some cases, as recommended by the manufacturer), the engine’s lifespan can be extended.

Monitoring Oil Levels and Quality

In some passenger cars, engine manufacturers specify that there is a loss of oil over time. One manufacturer, Audi specifies that owners should top up 0.5 liters of oil every 1000km. As one can imagine, if there is no top-up or oil replenishment, the oil levels can fall below the minimum value, causing damage to the engine.

Hence, it is essential to follow your manufacturer’s recommendations for topping up your engine to prevent damage. These top-ups also serve to replenish some of the used additives, providing additional protection for your engine.

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Automotive / Oil Properties / Strategic Tips

Understanding the Different Engine Oil Change Intervals

At the beginning of this article, we reiterated that there are more than 5000 models of engines that exist. Every engine was built to different specifications, but they all provide the user with the ability to move the vehicle. With different manufacturers, there will also be varying oil specifications for each model, including the recommended oil change intervals. Let’s look at some of those.

Factors Affecting Oil Change Frequency

Lubricants are designed for certain conditions; however, if those conditions are exceeded, then the lubricant can degrade at a faster rate. For instance, if the driver frequently starts and stops or experiences prolonged periods of idling, these patterns can stress the oil more quickly, causing it to degrade.

Understanding the Different Engine Oil Change Intervals

If the fuel quality is not as expected, it may also contribute to the oil degrading more quickly. In such cases, users may opt for shorter oil change intervals to ensure their engine remains protected.

Another factor affecting the frequency of oil changes is the quality of the oil used. Typically, synthetic oils may have longer oil change intervals than mineral oils. However, there are some cases where the manufacturers advise the same interval length, whether mineral or synthetic.

Using Oil Analysis to Determine Engine Oil Life

There are instances where the oil drain interval can be extended beyond the manufacturer’s recommended interval. However, this must be done with guidance from a lab while utilizing oil analysis. Typically, some applications do not utilize the additives in the oil as quickly and may not require the regular oil change interval; instead, the oil remains healthy by the time it’s supposed to be discarded.

This can be considered a waste of resources. With oil analysis, one can monitor the health of the oil and determine if it is nearing the end of its useful life, allowing for informed decisions on whether to change it or not.

The Debate over Extended Oil Change Intervals

There will always be a debate over whether it is wise to extend the oil change intervals for equipment, as it goes against the manufacturer’s recommendations (or, in some cases, this could void the warranty). However, just as with blood testing (or condition monitoring for oil), close monitoring allows us to justify the outcomes of extending the intervals.

Some of the benefits of extending the intervals include reduced manpower, allowing staff to perform other critical duties, a reduction in oil consumption and its disposal, as well as reduced downtime for maintenance. One can also include the reduction of safety risk depending on the application. These all add up in the end, and the benefits of safely extending the intervals may outweigh remaining at the recommended intervals.

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Automotive / Oil Properties / Strategic Tips

Benefits of Using the Right Engine Oil

As we’ve covered in this article, various types of engines require different levels of performance, and engine oils have been specifically designed for these conditions. Hence, it becomes critical to select the right engine oil for your engine. But what are some of the benefits of selecting the right oil?

Improved Fuel Efficiency

Firstly, the primary purpose of a lubricant is to reduce friction between contacting surfaces. By reducing the friction, a smaller amount of energy is required to perform the same amount of work. Overall, this leads to a more efficient system.

When we’re talking about engines, fuel is also required to produce energy for the engine to work. As engine oils have become more advanced, they have enabled significant improvements in fuel efficiency for many engines. This is one of the requirements in the API service categories. By selecting the incorrect viscosity of oil or type of oil for your vehicle, you can negatively impact the fuel efficiency, which in turn adds up to a higher fuel bill at the end of the month!

Longer Engine Life

The occurrence of wear is one of the most common challenges with engines. By using the correct oil (as recommended by the manufacturer), the viscosity of the oil is ideal for keeping the engine surfaces from touching, which can prevent wear.

Additionally, engine oils contain additives that can also help protect the oil and the engine’s components. Hence, with the right oil (as specified by your OEM), your engine will have the ideal conditions it needs to last longer compared to using an oil that does not provide the optimal protection.

Better Engine Performance

Engines were created with particular standards in mind. OEMs designed engines to withstand certain temperatures and conditions. These attributes are passed to lubricant suppliers who would design engine oils capable of withstanding and performing in these conditions. Using the recommended engine oil ensures better engine performance.

For instance, if the customer decides to use an API CK4 oil in their diesel engine but uses 500 ppm sulphur fuel, they can run the risk of poisoning their catalyst or damaging their aftertreatment devices. This would not lead to better engine performance! Therefore, it is essential to follow the OEM’s recommendations to achieve optimal engine performance.

Reduced Emissions

Many of the newer specified oils are designed to reduce emissions. However, the older spec oils were not developed with reducing emissions in mind. Hence, using an older-specification oil (API SL) in a vehicle manufactured in 2024 may not necessarily help reduce emissions. On the other hand, the API SP oil is designed with enhanced emission control in mind, making it ideal for reducing emissions.

Enhanced Lubrication and Protection

If we recall the straw example from earlier in this article, we will realize that engines have been designed for specific lubricants, both in terms of viscosity and additive packages. By using the recommended lubricants, we can ensure that our engines receive the necessary protection and have the correct amount of lubrication to prevent wear. Use lubricants specifically designed for your engine to ensure enhanced lubrication and protection.

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Automotive / Oil Properties / Strategic Tips

Types of Engine Oils

When you walk into the auto repair store, it can be quite overwhelming with the barrage of oils readily available for customers. It’s easy to get distracted by the shiny packaging or marketing claims (‘This is the best oil ever!’) when deciding to purchase oil for your vehicle. However, it begins with understanding the basics of engine oils.

Conventional Oil

This is the oil that has been around since the beginning of the automotive revolution. They are also referred to as mineral oils and represent the API Groups I-III base oils. Ideally, these oils can be traditionally found as the base for lubricants that are on the higher end of the viscosity spectrum (think 40, 50, and 60 weight).

These mineral oils are found on the earth, and their molecules may not all be the same size (unlike synthetic oils). They are usually less costly than synthetic oils but still provide some protection to the engines.

Synthetic Oil

Synthetics are considered the top-tier set of lubricants, as they can withstand harsher conditions compared to mineral oils. They are found in groups IV and V, and many of them are man-made, while others are naturally occurring. Most of their molecules are the same size, allowing for better properties, and they tend to be more expensive than mineral / conventional oils.

Synthetic Blend Oil

A synthetic blend oil refers to an oil that contains both synthetic and mineral base oils. However, there is no set ratio of synthetic to mineral oil that can impact the final performance of the lubricant to be classified as a synthetic blend. Many manufacturers can easily get away with using only 1% synthetic oil blended with 99% mineral oil and still label the oil as a “Synthetic blend.”

This gives the customer the false impression that they are purchasing an oil that will offer the best of both worlds.

High Mileage Oil

Until about a decade ago, high-mileage oils were not really that popular, but with the aging population of automobiles, there has been a significant increase in the purchase of this type of oil. Different manufacturers have varying specifications for these oils and typically use the vehicle’s mileage range to help guide customers in selecting the correct oil.

These oils are blended on the “thicker” side of the viscosity range, meaning on the higher end of the maximum viscosity. For instance, a regular 10w40 would appear to be “thinner” than a High Mileage 10w40. They are also reinforced with seal conditioners to help some of the seals in the older engines. But it does not contain magic, so it can’t repair your engine!

Racing Oil

The performance required of a Ferrari compared to that required of a minivan can differ drastically. The operating conditions are starkly different, and the engines would require specifications from their manufacturers. As such, there are specially developed racing oils for these higher-performance vehicles built to withstand harsher conditions compared to the regular engines.

This does not mean that you should use racing oil in your regular vehicle to get the performance of a race car. The oils are blended for specific purposes and must be used accordingly to ensure maximum functionality. Similarly, the oil used in the minivan would not be able to withstand the conditions of a racing car. Use oil that is compatible with the type of engine and the required performance.

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Automotive / Oil Properties / Strategic Tips

Understanding Viscosity and Engine Oil Grades

Engine oil is a lubricating fluid designed to reduce friction and wear between moving parts inside an internal combustion engine, while also cooling, cleaning, and protecting components from corrosion and deposits.

While we may think that there are numerous car manufacturers globally, as of 2025, there are only slightly over 100 original equipment manufacturers (OEMs), but over 5,000 models. Whether it’s a luxury vehicle or a basic, functional one, they all require one thing to keep them running: lubricants (in the EV market, this can mean greases as opposed to traditional oils).

Parallel to the various models of vehicles, there are also numerous types of lubricants on the market, each designed specifically for different requirements. In this article, we will share some knowledge on the areas you need to be familiar with for these types of lubricants, and of course, what impacts they have on your vehicle of choice.

Understanding Viscosity and Engine Oil Grades

Before exploring the types of oils, it is essential to understand one of the most important characteristics of oil: its viscosity. This is what governs the engine’s functionality and, to some extent, dictates its performance.

What is Viscosity?

Oil viscosity is the internal friction within an oil that resists its flow. It measures the oil’s resistance to flow and is one of the most important factors in lubricants. Viscosity is also defined as the ratio of shear stress (pressure) to shear rate (flow rate).

The SAE Viscosity Rating System

The SAE (Society of Automotive Engineers) developed viscosity grades to classify engine oils, enabling engine manufacturers and oil marketers to make recommendations and label their products accordingly. The SAE J300 is a series of two viscosity grades: one with the W and one without the W.

Monogrades with the letter “W” are defined by maximum low-temperature cranking and pumping viscosities and a minimum kinematic viscosity at 100°C. (Typically, this represents the start-up condition of an engine.)

Monogrades without the W are based on a set of minimum and maximum kinematic viscosities at 100°C and a minimum high temperature / high shear measured at 150°C and 1 million reciprocal seconds (s^-1). (Typically, this represents the operating conditions of the engine when it is in use.)

Multiple viscosity grade oils or multigrades are defined by:

Maximum low-temperature cranking and pumping viscosities
A kinematic viscosity at 100°C that falls within the prescribed range of one of the non-W grade classifications
A minimum high temperature / high shear viscosity at 150°C and 1 million reciprocal seconds (s^-1).

These represent the extremes of startup and engine operation.

The table below gives a summary of these.

Figure 1: SAE J300 revised January 2015. Source Widman International SRL

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Oil Properties

What are some innovations and future trends of Viscosity Index Improvers?

Innovations in Viscosity Index Improvers

As per Mortier, Fox, & Orszulik (2010), the three most important commercial VII families represent critical commercial techniques for manufacturing high molecular weight polymers. These are polymethacrylates produced by free radical chemistry, olefin copolymers produced by Ziegler chemistry, and hydrogenated styrene-diene or copolymers produced by anionic polymerization. While they are critical, these formulations will not be discussed in detail in this article, but we will take a look at some of the innovations within this space.

PARATONE®a, a family of viscosity index improvers currently belonging to Chevron Oronite, boasts of having developed the first Olefin Copolymer VII (Mid Continental Chemical Company Inc, 2024). However, upon further investigation, it must be noted that Exxon Chemicals was the original developer behind this product. Back in 1998, Oronite Additives, a division of Chevron Chemical Co. LLC, acquired the assets of Exxon Chemical’s Paratone crankcase olefin copolymer (OCP) Viscosity Index Improver Business (Chevron Chemical Co. LLC, 1988).

This particular Viscosity Index Improver has seen developments since the 1970s and offers solid and liquid VIIs for companies to include in their formulations (Chevron Oronite, 2024). It also allows improved formulating flexibility for developers, which can significantly reduce the costs involved or specialized base stocks depending on the product to be made. This is just one company that specializes in producing VIIs for the wider global market.

There are many other companies that have innovated in the Viscosity Index Improver space, but most of this work is patented as it involves heavy-balanced formulations. Other companies have also innovated on the production side of the VIIs by engineering equipment that can help produce a higher-quality VII.

Future Trends

(Future Market Insights, 2024) estimates the Viscosity Index Improver market will be USD 4.06B in 2024 and will increase to USD 5.39B by 2034. Additionally, in 2024, vehicle lubricants account for around 51.6% of the VII market. This is not just limited to the multigrade oils but includes transmission fluids, greases, and other oils. On the other hand, with the move towards more sustainable oils, Ethylene propylene Copolymer (OCP) is projected at a 30.4% industry share in 2024. Given the move towards more sustainable products, this is expected to increase.

If we take a global view of the compound annual growth rate (CAGR) per country to 2034, we can find some interesting facts. The United States shows a CAGR of 1.6%, with a heavy allocation towards more vehicle engine oil use and the manufacturing sector for pharmaceuticals and chemicals. On the other hand, Spain is projected to see a CAGR of 2.2% with auto manufacturers and power generation equipment (hydraulic oils, turbine oils, and greases).

Venturing to China, they have a CAGR of 3.2% due to the increased number of vehicles and significant industrialization. Their involvement in complex machinery will also drive this growth. The United Kingdom is positioned to see a CAGR of 1.1% resulting from its rise in high-performance engines and heavy industrialization. On the other hand, India should experience a CAGR of 4.3% with its high demand for industrial production, commerce, and automobiles.

Figure 2: CAGR% per country to 2034

With these positive CAGRs, it is conclusive that there will be a lot of growth within the VII industry. (Future Market Insights, 2024) also list some of the recent developments in the VII Market, which include:
In July 2023, Chevron Phillips Chemical announced a capacity expansion of its VII productions to meet the increasing demand for VIIs in the automotive and industrial sectors.
In April 2023, Lubrizol introduced a new line of viscosity index improvers (VIIs) for automotive lubricants, claiming to offer enhanced performance, including improved oxidation and thermal stability.
In March 2023, ABB completed the Marunda 2.0 oil blending plant extension project, doubling production capacity within three years despite challenges during the pandemic.
In October 2022, LCY Chemical Corp., a Taiwanese material science company, showcased its thermoplastic elastomer portfolio at K 2022. It highlighted its innovative approach to material science for a sustainable future, backed by a global distribution network.
In August 2022, Evonik’s Oil Additives division in CIS countries partnered with ADCO to enhance the energy productivity and effectiveness of industrial lubricants for construction, agriculture, mining, and manufacturing equipment.

From this, the future of Viscosity Index Improvers can only be enhanced by several of the major key players expanding their operations and innovating their creations to adapt to ever-evolving standards/guidelines set by OEMs and governments. As new regulations emerge regarding improved efficiency, increased oxidation stability, and thermal stability for lubricants, VII developers will be challenged to innovate new solutions for the lubricants to conform.

References

Chevron Chemical Co. LLC. (1988, October 08). Oronite Additives Acquires Exxon’s Paratone Viscosity Improver. Retrieved from Pharmaceutical Online: https://www.pharmaceuticalonline.com/doc/oronite-additives-acquires-exxons-paratone-vi-0001

Chevron Oronite. (2024, June 29). PARATONE® viscosity modifiers. Retrieved from Oronite: https://www.oronite.com/products-technology/paratone-products.html

Future Market Insights. (2024, April 15). Viscosity Index Improver Market Forecast by Vehicle and Industrial Lubricant for 2024 to 2034. Retrieved from Future Market Insights: https://www.futuremarketinsights.com/reports/viscosity-index-improvers-market

Gresham, R. M., & Totten, G. E. (2006). Lubrication and Maintenance of Industrial Machinery – Best Practices and Reliability. Boca Raton: CRC Press.

Mid Continental Chemical Company Inc. (2024, June 29). Viscosity Modifiers / Viscosity Improvers. Retrieved from Mid-Continental Chemical Company: https://www.mcchemical.com/lubricant-additives/viscosity-index-improvers

Mortier, R. M., Fox, M. F., & Orszulik, S. T. (2010). Chemistry and Technology of Lubricants – Third Edition. Dordrecht: Springer.

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Oil Properties

What impact do Viscosity Index Improvers have on Efficiency, Wear, and Degradation?

If we filled a swimming pool with honey during the winter when no heating was available, the honey would crystallize and become more viscous. Hence, if anyone tried to walk through the pool, moving would be difficult and require more energy. However, if heating was available to the pool, then the honey would be more fluid, and someone could walk a bit more freely (although still sticky at the end of the day!). As such, they would not have to exert as much energy.

The same applies to lubricants and their viscosities. If the lubricant is too viscous (thick honey in the winter), then more energy is required for the components while they are moving. For systems with varying temperatures, finding a lubricant that can maintain the desired viscosity for those changes is challenging.

However, with the invention of Viscosity index improvers, oils can now maintain a desired viscosity at variable temperatures. This significantly affects the energy the system requires and can reduce the energy needed, making some systems more efficient.

As such, the system’s overall efficiency is impacted, and less energy is required to overcome the internal frictional forces of the lubricant (as its viscosity remains within the required range). Passenger car engine oils saw this change with the integration of VIIs when multigrade oils were invented. They no longer needed one oil for summer and another oil for winter. This significantly saved many owners from draining and replacing their oils seasonally or finding their oil frozen in the winter!

Viscosity index improvers, therefore, enhance the overall efficiency of these systems by maintaining the lubricant’s viscosity throughout the changing temperatures. Subsequently, there is no need for additional heaters in the lube oil system, which would also require additional energy. This is another area where cost and energy savings can also be achieved.

Maintaining a particular viscosity at variable temperatures allows the lubricant to form a full film (also known as hydrodynamic or elastohydrodynamic lubrication) between the two surfaces, thus offering them protection from wear.

If the viscosity became reduced (due to an increase in temperature without the VII), then the lubricant would not form a full film or experience boundary or mixed lubrication. In this case, there is the potential for increased wear, which will negatively impact the components in the system. As such, using VIIs can also reduce the potential occurrence of wear or aid in reducing wear.

As per (Gresham & Totten, 2006), this does not mean that the viscosity never changes. When the viscosity of a lubricant changes, its viscosity index will change accordingly. If the viscosity index decreases, this can likely be because of the breakage of the polymeric Viscosity Index Improver polymer molecules to produce smaller chains, which essentially reduce its originally intended effect. If there is a reduction in the molecular weight of the VII, then the lubricant will see a reduced viscosity at both 40 & 100°C. This also reduces the temperature related viscosity effect.

Viscosity Index Improvers significantly improve a system’s overall efficiency and can help reduce wear. However, these additives can degrade over time with high temperatures and shear stress.

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Oil Properties

What is the role of Viscosity Index Improvers in Lubricants?

Viscosity Index Improvers began their commercial debut around the 1950s to accommodate the new developments in automotive oils, which were then adapting multigrade viscosities. However, they were used even before (back in the 1930s) when workers in crude distillation realized that small amounts of rubber improved the VI of the oil but also increased sludge formation.

Today, VIIs are still primarily used as engine lubricants. They can also be found in automatic transmission fluids, multipurpose tractor transmission fluids, power steering fluids, shock absorber fluids, hydraulic fluids, manual transmission fluids, rear axle lubricants, industrial gear oils, turbine engine oils, and aircraft piston engine oils. (Mortier, Fox, & Orszulik, 2010)

Essentially, VIIs try to maintain the oil’s viscosity at varying temperatures. They try to ensure that the oil does not experience a loss of viscosity, which can occur due to high temperature or shear. VIIs can be considered polymers, which are tightly wound coils. When temperature or shear is applied to these coils, they unravel (lose their viscosity). Depending on the amount of shear, they may never recover their original shape (or viscosity).

As seen in Figure 1 below, Mortier, Fox, & Orszulik (2010) describe the change in the shape of the VIIs as a result of high temperature or shear. They can coil and uncoil depending on the shear stress, but if the bonds are broken, they will not reform their original coil and lose their intended viscosity.

Figure 1: Mechanical Polymer Degradation (excerpted from (Mortier, Fox, & Orszulik, 2010)

Interestingly enough, it must be noted that some VIIs provide lubricants with additional functions of Pour point depression and dispersancy. This is highly dependent on their composition.

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Oil Properties

What are Viscosity Index Improvers?

Viscosity Index Improvers (VIIs) are additives that help maintain the viscosity of lubricating oils across a wide temperature range, ensuring consistent performance.

This article will explore the nature of viscosity index improvers and their role in industrial and automotive lubricants. We will also look at their impact on lubricant efficiency, innovations involving this type of additive, and future trends.

Before discussing the nature of viscosity index improvers, we need to understand the role of viscosity. Essentially, this is one of the most critical functions of a lubricant, as it directly affects its flow rate and ability to keep the two interacting surfaces apart.

By nature, all base oils have an assigned viscosity based on their blend. However, other properties are required when we’re creating finished industrial or automotive lubricants. For instance, we may need the oil to withstand higher temperatures while still maintaining a particular viscosity, which not only provides wear protection for the equipment but also flows at a rate that does not incur frictional losses. Those are a lot of functions!

Typically, as temperature increases, viscosity decreases, and as the temperature decreases, the viscosity increases. One example is the state of water: when heated, it can turn into a gas (lower viscosity), or when frozen, it can transform into ice (higher viscosity). However, depending on the type of material, there will be varying rates of viscosity change with temperature. The viscosity/temperature relationship is called the viscosity index (VI).

As per Mortier, Fox, & Orszulik (2010), the kinematic viscosity of oil is measured at 40°C and then at 100°C. The viscosity change is then compared with an empirical reference scale initially based on two sets of crude oils: a Pennsylvania crude arbitrarily assigned a VI of 100 and a Texas Gulf crude assigned a VI of 0.

The higher the VI, the less effect that temperature has on the oil, which means that the oil can maintain a particular viscosity for a longer time at a more extensive temperature range. This is ideal for lubricants in environments experiencing temperature changes. However, not all oils have a high viscosity index. Typically, paraffinic oils can have a very high viscosity index. On the other hand, naphthenic oils have a low or medium viscosity index. The table below gives an overview of the viscosity index for various oils.

Table 1: Viscosity index of API Groups I-III

When trying to manage or alter the viscosity index of the oils above, the use of Viscosity Index Improvers (VII) can help by adding that property to an oil to allow it to have other beneficial properties. As per (Mortier, Fox, & Orszulik, 2010), viscosity index improvers consist of five main classes of polymers:

Polymethylmethacrylates (PMAs).
Olefin copolymers (OCPs).
Hydrogenated poly (styrene-co-butadiene or isoprene) (HSD/SIP/HRIs).
Esterified polystyrene-co-maleic anhydride (SPEs)
A combination of PMA/OCP systems.

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