Viscosity Index? (Question)

The viscosity index (VI) is an arbitrary, unit-less measure of a fluid’s change in viscosity relative to temperature change. It is mostly used to characterize the viscosity-temperature behavior of lubricating oils. The higher the VI, the more stable the viscosity remains over temperature fluctuations.

Why is viscosity index important?

The VI is a dimensionless number, i.e. it has no physical unit. It allows for a better comparison of the viscosity behavior of different oils based on temperature. The viscosity index is important in order to ensure, e.g., the best possible lubrication for machinery, as temperature changes occur during operation.

What does a high viscosity index mean for an oil?

Oil viscosity index explained A higher viscosity implies a slower flow and a thicker fluid. The viscosity changes with temperature to ensure protection and operability under all circumstances. Thus, the viscosity index measures the ability of an engine oil to resist becoming thinner at high temperatures.

What is the unit of viscosity index?

While the VI has no units of measure, it is well known that the viscosity index of a conventional mineral oil is between 95 to 100. Highly refined mineral oils have a VI of approximately 120. Synthetics may have a VI of nearly 250.

Is higher viscosity index better?

Viscosity index diagram The slope of the lubricant with a high VI is more horizontal: the viscosity remains more stable across a wider temperature range. This means a lubricant with a higher viscosity index is more desirable, because it provides a more stable lubricating film over a wider temperature range.

What do viscosity numbers mean?

So what do the numbers mean? The number preceding the W designates the viscosity at a low temperature, and the number following represents viscosity when the engine is hot. For example, a 10W-30 motor oil means the viscosity is at 10W when the engine is cold and 30 when the engine is hot.

How do you read viscosity?

The lower the number, the less the oil thickens in cold weather. The numbers after the “XW” indicate viscosity at 100 degrees Celsius and represent the oil’s resistance to thinning at high temperatures. For instance, oil with a 5W-30 grade thickens less than oil with a 10W-30 grade in cold weather.

What is viscosity index Careerride?

ANSWER: effect of temperature on changes in viscosity.

What is VI improver?

VI improvers (also known as viscosity modifiers) are additives that increase the viscosity of the fluid throughout its useful temperature range. This article is meant to provide you with a better understanding of viscosity index improvers, what they are, what they do, and why they are important.

What does 5w30 mean?

5w30 is a motor oil that is widely used in light-duty petrol and diesel engines. Like most motor oils produced today, 5w30 is a multi-grade oil, meaning it ranges from a lower viscosity grade of 5 to a higher viscosity grade of 30.

What viscosity is 3 in 1 oil?

3-IN-ONE® Motor Oil is a SAE 20 special blend of high-grade oils engineered for 1/4 HP motors or larger. This long-lasting formula is great as an electric motor oil and lubricant, and can also be used to maintain sewing machines fans, drills, lawn tools, and more.

What is the difference between viscosity grade and viscosity index?

Viscosity is the most important parameter since the viscosity grade can be the difference between optimal performance and machine breakdown. Viscosity index is a measure of how much the viscosity will change as temperature rises or falls.

What is viscosity range?

In layman’s terms, viscosity defines a fluid’s resistance to flow. The higher the viscosity of a liquid, the thicker it is and the greater the resistance to flow. Temperature will affect the viscosity of most materials.

What is meant by viscosity and viscosity index?

Viscosity rating is a measure of the oil’s resistance to flow or thickness, and is the single most important characteristic of hydraulic oil. The viscosity index number indicates the extent of thickness, or resistance to flow, with temperature changes. As an example: 30W oil flows much faster at higher temperatures.

Don’t Ignore Viscosity Index When Selecting a Lubricant

The viscosity index (VI) is an important lubricant selection criterion that is much too frequently overlooked. One reason is because it is little understood by the general public. There is a common misconception that the viscosity index is included in the ISO Viscosity Grade, although this is not the case. In terms of lubricant performance differentiation, it is a stand-alone characteristic. We are all aware that the viscosity of a lubricant is the single most critical physical parameter to consider.

Viscosity is defined by the amount of friction created between molecules as a result of fluid movement.

In machines, the viscosity of the film influences the thickness and strength of the film.

The Implications of Viscosity In contrast, a lubricant’s viscosity is useless unless the temperature, or the temperature at which viscosity is determined, is also stated in the specification.

  1. The minimum, maximum, and optimal viscosity requirements requested by machines do not take temperature into consideration at any point.
  2. Remember that the well-known Stribeck curve does not have a temperature component, as you might expect.
  3. It is important to remember that the ISO Viscosity Grade system only measures viscosity at a single temperature: 40 degrees Celsius.
  4. The viscosity index (ASTM D2270) was established for this purpose by E.
  5. Davis in 1929 and is still in use today.
  6. A benchmark for low viscosity changeability relative to temperature was established using the technique with Pennsylvania crude (paraffinic) serving as an extreme example of low viscosity changeability relative to temperature.
  7. If a lubricant was found to be identical to Pennsylvania crude oil, it was given a VI of 100 rating.

There was a VI of 50 halfway between the two, and so on.

Temperatures ranging from 40 degrees Celsius to 100 degrees Celsius were utilized to calculate the VI.

These calculators can be used in a number of different ways.

Best of all, you may use a single known viscosity (and temperature) as well as VI (which is often available on a lubricant’s product data sheet) to determine the viscosity of the same lubricant at any other temperature (for example, the operating temperature of a machine).

Other lubricants can have VIs in the hundreds of thousands.

Allow me to demonstrate this with two different oils that have one thing in common: they are both ISO VG 150.

Now, let’s look at the viscosity of these oils at temperatures ranging from negative 20 degrees Celsius (minus 4 degrees Fahrenheit) to 100 degrees Celsius (212 degrees F). This is seen in the following table.

89% of lubrication professionals consider an oil’s viscosity index when selecting a lubricant, according to a recent survey at

When comparing the viscosities of the 95 VI oil with the 150 VI oil at minus 20 degrees Celsius, there is a 236 percent difference in viscosity and a minus 25 percent difference at 100 degrees Celsius. At 40 degrees Celsius, there is, of course, no difference. In addition to the design and operation parameters of the machine, as previously stated, the machine defines the viscosity needs. These circumstances have an impact on temperature, which in turn has an impact on viscosity, which has an impact on the protection given.

  • Outdoor mobile equipment is often capable of operating in these difficult circumstances.
  • Instead, using real field data and a trial-and-error technique, the optimal viscosity is determined using a mathematical model (simply testing with different viscosity oils and measuring temperature and wear protection).
  • Because of either churning losses (too much viscosity) or mechanical friction, oil with a viscosity that is lower or higher than the ideal viscosity will generally raise the stable temperature of the oil in a given amount of time (too little viscosity).
  • The more the variability of the environment, the greater the demand for high VI oils.
  • The decision of viscosity is more of a random guess.
  • Remember that the ISO Viscosity Grade System (ISO 3448) is based on 50-percent increments between grades, therefore you must take this into consideration.
  • Choosing a precise lubricant might be tough when the viscosity alternatives are all 50 percent distant from one another.
  • This is yet another incentive to use lubricants with a high VI rating.
  • For example, highly refined and pure mineral oils will have higher VIs than less refined and less pure mineral oils.
  • Keep in mind that oils containing VI improvers, particularly those of specific kinds, are more susceptible to irreversible loss of VI and viscosity over time.

The viscosity index values are listed on practically all product data sheets for lubricants that are commercially accessible. Because this basic number is there, it should be taken into consideration when creating specifications for lubricants in virtually all machine applications.

Understanding the viscosity index of a lubricant

In terms of performance and long-term durability of your gear, the viscosity of your lubricant is quite important. If you choose a lubricant with the suitable viscosity index for your application, you may save downtime and maintenance expenses. When it comes to lubricants, their viscosity is defined as their resistance to flow and shear. It is impacted by a variety of factors, including contamination with water, particulates, or other lubricants, but it may also be affected by the age of the oil.

In contrast to kinematic viscosity, which describes how fast the lubricant flows when force is applied, dynamic viscosity provides information on the force required to make the lubricant flow (also known as absolute viscosity).

What is the viscosity index (VI) of a lubricant?

Generally speaking, temperature has an effect on the viscosity of a lubricant; in general, greater temperatures result in lower viscosities. What influences how much the viscosity of a lubricant decreases with increasing temperature is the formulation and quality of the lubricant. The viscosity index (VI) of a lubricant is the rate at which the viscosity changes as a result of a change in temperature. You must comprehend the VI in order to determine if a lubricant fits the criteria of an asset depending on the operating temperature range.

See also:  Absolute viscosity — Dynamic viscosity? (Solution)

How is the viscosity index of a lubricant determined?

Generally speaking, temperature has an effect on the viscosity of a lubricant; in general, higher temperatures result in lesser viscosity. The amount by which the viscosity decreases with increasing temperature is determined by the formulation and quality of the lubricant. Temperature changes have an effect on the viscosity of lubricants, which is measured by their viscosity index (VI). It is necessary to understand the VI in order to determine if a lubricant satisfies the needs of the asset based on its operating temperature range.

Viscosity index diagram

The picture below illustrates how the viscosity (vertical axis) of two different lubricants changes in response to temperature variations (horizontal axis). It has a more horizontal slope than the other two, which means that the viscosity is less volatile across a larger temperature range when the VI is high. The greater the viscosity index, the better, since it offers a more stable lubricating coating across a broader temperature range, which makes it more attractive.

The risks of lubricants with low VI

Even while lubricants with a lower viscosity index may have the right viscosity at a certain temperature, their viscosity might decrease dramatically as the temperature rises.

Mechanical friction and wear can be increased as a result of film loss, which can cause an increase in both. Poor viscosity index (VI) lubricants may have excessive viscosity when used at lower temperatures, leading in low oil flow, oil starvation, and dry start-ups.

Always check the VI of a lubricant

Manufacturers can improve the viscosity index of a lubricant by including certain additives into the formulation. It is possible to develop a lubricant to fulfill the criteria of the original equipment manufacturer in this manner. Whenever possible, we recommend that you consult the requirements of the equipment manufacturer when selecting a lubricant for your particular application. Climate and operation conditions of your machinery must be taken into consideration. Machines that are properly lubricated and have an accurate VI will work better and last longer if they are properly lubricated.

Q8Oils offers lubricants with high VI

The following are some examples of high VI products available from the Q8Oils product line: The Q8 Handelhydraulic oil series is designed to be used in a wide variety of temperature and application conditions. This hydraulic oil offers remarkable flow characteristics as a result of its extremely high viscosity index of 180. The excellent oxidation stability ensures that the drain interval and lubricant life are both prolonged. The Q8 Voltasynthetic Turbine Oil Series is being developed for use in both steam and gas turbines, among other uses (and combined cycle applications).

Viscosity index 130 indicates that the viscosity is steady across a wide range of temperatures.

What is Viscosity Index? — Twin Specialties Corp.

If you are studying lubricants, there are a number of elements to consider before making your final decision, including the viscosity of the lubricant, its flashpoint and pour point, and its oxidation stability. The viscosity of the solution is the most significant parameter since the viscosity grade might mean the difference between optimal performance and complete machine failure. When measured at 400 degrees Celsius, the ISO Viscosity Grade (VG) is calculated; however, it will vary depending on the operational temperature.

Viscosity Index Explained

The requirements for viscosity are based on factors such as component design, loads, and operating speed. The operating temperatures and temperature ranges of the machines are not taken into consideration while making machine recommendations. As a result, while selecting a viscosity, it is critical to take into consideration the usual operating temperature. For the purpose of adjusting for temperature changes, the viscosity index was established, which measures the stability of viscosity under varying temperatures.

  1. The larger the viscosity index of a lubricant, the better the stability of the lubricant’s viscosity, and vice versa.
  2. When temperatures reach severe highs and lows, the difference between Oil A and Oil B becomes even more noticeable.
  3. Oil A, on the other hand, changes much more and may have a negative impact on performance when exposed to high temperatures.
  4. It is possible to find Viscosity Indexes (which can be found on most product data sheets) ranging from 90 to 160.
  5. The viscosity index can also provide information about the type of base oil used and the quality of the oil.
  6. Some lubricants may have viscosity-index improver additives to aid in the stabilization of the lubricant under high-temperature situations.

When the temperature is raised, the molecules uncoil and thicken the oil, which helps to keep the viscosity stable. It is crucial to remember, however, that oils containing VI-improvers will experience a permanent loss in VI and viscosity as the oil ages.

When Should You Opt for Higher VI

The viscosity index of the lubricant should be increased if the loads, temperatures, and speeds of your activities are likely to change over time, as well as if there are other environmental factors. The viscosity of the lubricant will change as a result of the changes in these factors. As a result, it is critical to invest in a lubricant that will retain an appropriate viscosity under a variety of working situations. In contrast, if your operation is pretty constant, it may be more cost-effective for you to use a lubricant with a lower viscosity index in order to conserve money.

Finding the precise ideal viscosity becomes considerably more challenging when dealing with such big increments of time.

Calculating VI

If you are unclear of the viscosity or viscosity index of a lubricant, there are online calculators that can assist you. You may find out the viscosity index by entering the viscosity at two different temperatures and the viscosity index will be calculated for you. It is possible to determine the viscosity at a specific temperature using a previously determined viscosity, previously determined temperature, and previously determined viscosity index to determine the required temperature to determine the new viscosity.

Key Takeaways

To summarize, some of the most important reasons to use a lubricant with a higher viscosity index are as follows:

  • It is impossible to determine the optimal operating viscosity. The use of variable operating temperatures and/or the use of severe operating temperatures Other operational characteristics, such as speed and load, are also taken into consideration. You wish to improve the efficiency of your energy use. You wish to lengthen the oil service life as well as the machine service life.

The majority of these entail enhancing performance that may be negatively impacted by operating uncertainty. In these situations, it is preferable to use lubricants with a greater viscosity index (VI). It may be advantageous to your bottom line to use cost-effective lower VI lubricants in the following situations:

  • Constant speeds and loads are required. The temperature at which the machine operates remains constant. The optimal viscosity has been identified and can be reliably achieved

If your working procedure is more predictable, it may not be essential to invest in a lubricant with a higher viscosity index (VI). It is critical to assess your operating procedures and reference machine manuals in order to fully comprehend your operating circumstances and requirements. The use of a greater viscosity index can help to smooth out operations and improve performance throughout a wide range of loads, speeds, and temperatures if you are dealing with uncertainty and variable in your operations.


Recent Web-based illustrations The viscosity index of an oil measures how resistant it is to weakening when exposed to higher temperatures. —Paul Weissler, Popular Mechanics, published on August 31, 2020 The viscosity index is a measure of the resistance to thinning as a function of temperature. When the resistance to thinning increases with rising temperature, this is characterized as viscosity index (Paul Weissler, Popular Mechanics, 14 February 2019). When the resistance to thinning increases with rising temperature, this is characterized as viscosity index (Paul Weissler, Popular Mechanics, 14 February 2019).

14 February 2019: Paul Weissler, Popular Mechanics, 14 February 2019: The viscosity index is a measure of the resistance to thinning as a function of temperature.

When the resistance to thinning increases with rising temperature, this is characterized as viscosity index (Paul Weissler, Popular Mechanics, 14 February 2019).

Please provide comments.

Viscosity Index: Definition & Formula

Saran NarangSaran has extensive consulting experience as a result of his Bachelor of Science in Mechanical Engineering degree. Take a look at my bio Christianlly Cena is a fictional character created by author Christianlly Cena. Christianlly has experience as a college physics instructor and as a laboratory course facilitator. He holds a master’s degree in physics and is currently pursuing his PhD in the field of physics. Take a look at my bio The viscosity index of a fluid plays an important role in determining which lubricant is best for safeguarding your car’s engine.

07/07/2021 – This page has been updated.

Defining Viscosity Index

Before we can understand the viscosity index, we must first grasp the concept of viscosity, which is a physical characteristic of fluids. Everything – from the tires of a car to the water in a pond – is composed of the substance known as matter. But they don’t all have the same appearance, do they? This is due to the fact that they are various states of matter, with solids, liquids, and gases being the most frequent. Liquids Gases are distinguished by their capacity to flow and conform to the shape of the container in which they are confined – for example, a glass of water.

  1. The viscosity of a fluid is a measure of the fluid’s resistance to flow.
  2. Honey is more viscous than water, for example, indicating that it is thicker than the latter liquid.
  3. Then there’s the question of what exactly is the viscosity index, as well as the relationship between the two.
  4. The viscosity indexis a measure of the change in viscosity that occurs as a result of temperature changes.
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Where Does Viscosity Come From?

Before we can comprehend why temperature has an effect on viscosity, it is necessary to understand where the viscosity of a fluid originates from. Take whatever river you’ve ever seen and run with it. Consider it as a stack of hundreds of super-thin sheets of water that are all moving at different speeds but all coming together as a single mass. The molecules in each sheet number in the millions, and the molecules in each sheet are constantly flowing into sheets above and below. Viscosity is caused by the difference in speeds between the sheets as a result of friction, which is compounded by the millions of molecular interactions that take place.

Shear tension is created between sheets as they move at various speeds. Shear stress is caused by the movement of sheets at different rates.

Temperature and Viscosity

What about the temperature, then? Whenever you measure the temperature of something, you are effectively measuring the average kinetic energy of all the molecules in that particular piece of matter. The higher the temperature of anything, the greater the amount of energy and movement the molecules have. Consider the case of boiling water: when the water molecules heat up, their energy and mobility increase to the point where the water begins to bubble. You should be able to see clearly now that a change in the energy of the molecules (temperature) will result in a change in the rate of movement of molecules between the sheets of a liquid.


Given the fact that every fluid is unique, each fluid’s reaction to the same temperature will be distinct, which is why the viscosity index is important.

In the case of lubricating oils, the viscosity of the oil at 100 degrees Fahrenheit would be substantially different from the viscosity of the oil at 200 degrees Fahrenheit.

The Equation

Viscosity indices are most typically utilized in the case of hydraulic and lubricating oils, among other things. The viscosity index, abbreviated as VI, of any oil may be calculated using the following equation:

Viscosity Index: Fill-in-the-Blank Activity

This task will assist you in determining your level of understanding of the definition and relevance of the viscosity index.


Print or copy this page onto a piece of blank paper to use for this exercise. Then, to complete each of the sentences that have been provided, utilize the terms from the word bank. Please neatly type your responses on the available blank area.

Word Bank

A physical quantity relating to the average kinetic energy of molecules in a material is denoted by the symbol . In the presence of high viscosities, laminar flow occurs when fluid particles travel in the same direction, passing each other without mixing. A quantity that expresses the amount of a fluid’s resistance to motion is denoted by the symbol . In most cases, the term is used to distinguish between the viscosity-temperature behavior of lubricating oils and 5. In order to function as a Bridge between metals, an automobile engine makes use of viscous lubricants.

When the temperature of a fluid is , the viscosity of the fluid is .

A liquid with a VI rating may survive significant temperature fluctuations.

The viscosity of any fluid will continue to alter as the temperature of the fluid increases.

Answer Key

Temperature is number one. 2. sheets of paper Stickiness, viscosity index, and hydraulic viscosity 5. act as a buffer 6. grows in value, falls in value 7. is really high8. varies

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Oil Viscosity Index and Viscosity Temperature Relation

Viscosity is a measure of how resistant a lubricating oil is to flowing. From the perspective of Hydrodynamic Lubrication Theory, viscosity plays a critical part in the lubrication regime experienced in the machine element – the greater the viscosity, the thicker the oil film that prevents the surfaces from coming into contact with one another. However, it is also well known that temperature has an effect on viscosity levels. This feature of lubricating oils and/or greases is one of the most critical determinants of how well they operate in mechanical systems when exposed to high temperatures and high viscosities.

  • When the temperature of the oil rises, the viscosity of the oil frequently decreases rapidly.
  • Temperature rise owing to friction-induced heating is unavoidable in tribology systems (e.g., gears, bearings, and engines).
  • The viscosity of the lubricant, on the other hand, might be crucial for the performance of applications in sub-zero temperatures.
  • As a result, neither a thick nor a thin lubricant may be considered as the most appropriate choice by an engineer when making the lubricant selection decision.
  • Attempts have been made over the years to construct empirical relationships to characterize the temperature-viscosity behavior of lubricants.
  • When written out, the equation looks to be as easy as:where is dynamic viscosity and and are empirical constants.
  • An other significant equation was derived by Walther in 1928:whereis the kinematic viscosity, and, and, and, and, and, and, and are empirical constants.
  • The equation appears to be unsatisfactory to any math-savvy readers; nonetheless, it is effective for a big class of petroleum oils over a wide range of temperaturetos and is applicable to a wide range of temperatures.
  • Vogel also presented the following model, in which the variables x, y, and z are empirical constants: Engineering calculations and predictive numerical models find this model to be more beneficial than the previous one.
  • The reason for this uncertainty is due to the fact that each of these equations requires a large amount of experimental data in order to be correctly fitted.

In layman’s terms, empirical relationships do not meet the demand for a preset measure for viscosity-temperature characteristics for a typical lubricant user who is looking for a premade meter.

Temperature – Viscosity Calculator

A simple calculator that can be used to calculate the dynamic viscosity of an oil at operating temperature if the dynamic viscosities at two other temperatures are known (typically, the viscosities at 40 degrees Celsius and 100 degrees Celsius are taken from the data sheet as reference points, but any two temperatures and viscosities can be used). As a matter of thumb, the viscosity of a machine oil decreases by approximately 25% for every 10 degrees Celsius increase in temperature. Close to the reference sites, the Reynolds interpolation function performs well in terms of accuracy.

Oil Viscosity Index Definition

Dan and Davis coined the term “viscosity index” in 1929 to describe the way in which different oils’ temperature-viscosity correlations differed from one another. In the early days of industrial lubrication, it was discovered that lubricants manufactured from Pennsylvania crude oil are less sensitive to temperature than lubricants made from Golf Coast crude oil, despite the fact that they both had the same kinematic viscosity at 100 degrees Fahrenheit. As a result, these two groups were initially labeled as reference oils, with the former being awarded a viscosity value of 100 and the latter being allocated a viscosity index of 0.

Since then, this index has gained widespread popularity and has shown to be quite beneficial for a variety of experts, ranging from lubricant manufacturers to everyday lubricant users.

The viscosity index of a lubricant is a mathematical representation of the relative behavior of a lubricant’s temperature-viscosity behavior in comparison to two reference oils.

The viscosity index is represented graphically in the figure below.

Viscosity Index Formula

The following is an outline of a stepwise approach for estimating the viscosity index, VI: VI estimate using a graphical representation (see figure). It is vital to note that a higher VI indicates that the oil’s kinematic viscosity is less susceptible to temperature; as a result, the lubricant is likely to function better throughout a wider temperature range. In contrast, when the viscosity of the lubricant is low, the viscosity of the lubricant may decrease fast with an increase in temperature.

It is interesting to note that the VI may rise over 100 if the value of in the preceding figure appears between and.

It is vital to understand that the performance of a lubricant VI may be enhanced by using selected additives in the lubricant composition.

These polymer additives are frequently used to increase the viscosity index of multi-grade oils, which is a popular use.

A low VI oil should be used when the operating parameters of the machineries are almost constant (for example, in household applications); however, a high VI oil should be used when the load and operating parameters of the machineries are highly fluctuating (for example, in excavators and automobiles).

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On the whole, the relevance of knowing the temperature-viscosity connection in industrial lubrication methods is generally known.

When it comes to practical applications, empirical connections are valuable for mathematical calculations and engineering design. However, the viscosity index has been widely acknowledged and promoted as a highly useful measure for determining the temperature-viscosity behavior of lubricants.

Viscosity Index Calculator

Here is a simple calculator that may be used to calculate the viscosity index (VI) based on the kinematic viscosities:

Classification of Viscosity Indexes of Oils

Viscosity index Classification
Under 35 Low
35-80 Medium
80-110 High
Over 110 Very High

Video Explaining Viscosity Index

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  1. The ASTM Standard Practice for Viscosity-Temperature Charts for Liquid Petroleum Products, published by ASTM International in 2003 and available at
  2. Wright, A., 1969, An Improved Viscosity-Temperature Chart for Hydrocarbons, Journal of Materials, 4(1), pp. 19–27
  3. Stachowiak, G. W., and Batchelor, W., 2000,Engineering Tribology (Second Edition),

Viscosity Index Calculator

To determine the viscosity index of an oil, we must know the viscosity of the oil at both 40°C and 100°C. Table 1 is the first row of the first row. In the first row, enter kinematic viscosity (KV) at 40 degrees Celsius. In the second row, enter kinematic viscosity (KV) at 100 degrees Celsius. To obtain the viscosity index, press the Calculate button (VI). Finally, press theClearbutton to begin the process over.

Calculate Viscosity @100°C

Another option is to compute kinematic viscosity by dividing the viscosity index by two. It is feasible to compute viscosity at 100 degrees Celsius using a given viscosity index (VI) and viscosity at 40 degrees Celsius. For example, the viscosity index (VI) should be entered in the first row of the second table. In the second row, enter kinematic viscosity (KV) at 40 degrees Celsius. To find out how much KV @100°C you have, click Calculate. As previously noted, the Clear button can be used to begin a new computation process.

Calculate Viscosity @40°C

Calculate viscosity (KV) at 40 degrees Celsius in the same way, using calculator 3. Table 3 contains the known viscosity index (VI) and kinematic viscosity (KV) at 100 degrees Celsius. To compute kinematic viscosity (KV) at 40 degrees Celsius, use the Calculate button. As before, click on the Clear button to start again and generate a fresh viscosity calculation.

Lubricants Viscosity and Viscosity index

At a particular temperature, a fluid’s viscosity is defined as its resistance to flow. To calculate viscosity, it is common practice to sample oil and fluids at the same temperature to ensure consistency. Low viscosity fluids (fluids that move freely and quickly) flow or pour more easily and quickly. As a result, high viscosity fluids flow more slowly and with less ease. If the viscosity of the fluid is high, it will almost certainly be difficult to pour. Fluid with a high viscosity has greater barrier to flow than fluid with a low viscosity.

Q: What is viscosity index?

A:The viscosity index of a fluid is a numerical value determined in accordance with ASTM D2270 or ISO 2909 standards. The viscosity index is a measure of how much a fluid’s viscosity changes in response to temperature changes. It is an arbitrary unit of measurement with no unit of measurement. As a result, a greater viscosity index (VI) indicates that the fluid is more stable and exhibits less fluctuations in viscosity throughout a wider temperature range.

Q: How to calculate viscosity index?

A: The viscosity index of a fluid (often oil) is computed by comparing the viscosity of the fluid at 40 and 100 degrees Celsius. The ASTM D2270 and ISO 2909 are two commonly used techniques for calculating viscosity index.

For example, to determine the viscosity index, we may utilize an online viscosity index calculator or Excel tools, as shown below. A viscosity index calculator of this type may be found at the following website:

Afton Viscosity Index Improvers, Product Article

One of the most significant features of an efficient and long-lasting lubricant is the regulation of viscosity as a function of temperature change. Numerous applications that cycle between cold and hot operating temperatures require the same amount of lubrication and protection throughout the operation. Polymer-based viscosity index improvers from Afton are useful in a wide range of mineral oil lubricant applications and are available in a variety of formulations.

What is a Viscosity Index Improver and What Does it Do?

To put it another way, a viscosity index improver (VII), also known as a viscosity modifier, prevents a lubricant from becoming too “thin” when exposed to high temperatures. Consider the consistency of honey in a glass – at low temperatures, the liquid is sticky and thick. After being subjected to heat, honey, on the other hand, flows considerably more quickly and has a lower viscosity than before. When the viscosity of a lubricant falls and becomes excessively thin, the protective characteristics of the lubricant are reduced, which results in equipment damage and wear.

In this manner, it is ensured that the lubricant protects the equipment completely at both low and high temperatures.

When selecting the most appropriate viscosity index improver, it is critical to evaluate the specific needs of the completed product.

High molecular weight polymers have better thickening efficiency but are more susceptible to mechanical shear.

Afton Additive Solutions

As part of their HiTEC® Performance Additive product line, Afton offers a variety of Olefin Copolymer (OCP) viscosity index improvers (VII) for use in a variety of applications. In addition to being available in both liquid and solid forms, OCP viscosity index improvers are also oil soluble and may be used with a wide range of lubricant formulations. Many OCP viscosity improvers are suggested for use in engine lubricants, and some are even FDA-approved. In order to manufacture multi-grade high performance engine oils, an OCP polymer is typically combined with a detergent package and a pour point depressant, among other ingredients.

Olefin Copolymer (OCP) Additives

Afton also sells a number of viscosity index improvers (VII) based on Polymethacrylate (PMA) that may be used in a variety of industrial and automotive lubricant compositions, including hydraulic fluids.

When it comes to applications requiring high shear stability, polymethacrylate polymers are often suggested, such as driveline lubricants and shear stable hydraulic fluids.

HiTEC® Grade Chemistry Type Viscosity @ 100°C Typical Application(s)
HiTEC ®5708 Non-Dispersant PMA 1500 mm 2 /s Hydraulic Fluids
HiTEC ®5710 Dispersant PMA 850 mm 2 /s Transmission Fluids
HiTEC ®5724 Non-Dispersant PMA 1250 cSt Hydraulic Fluids
HiTEC ®5736A Non-Dispersant PMA 775 cSt Shock Absorber FluidsOther Industrial Use
HiTEC ®5738 Dispersant PMA 620 cSt Transmission Fluids
HiTEC ®5739 Non-Dispersant PMA 575 cSt Hydraulic Fluids
HiTEC ®5785H Non-Dispersant PMA 1200 cSt Hydraulic Fluids

More than Just Lubricants

The HiTEC® Viscosity Index Improvers from Afton can be used in a wide range of applications that are not connected to lubricants. The polymers can be used to thicken or increase the viscosity of a variety of various product formulations and manufacturing processes, among other things. Interested in learning more about Afton HiTEC® polymeric additives or obtaining a sample? Contact us today to request a sample of our polymeric additives.

Understanding Viscosity Index

We use the term Viscosity Index (VI) to refer to a data point reference on our technical data sheets. The Society of Automotive Engineers (SAE) in the United States was the first organization to develop the VI data point or scale. When lubricating oils (or base oils, if they are used to make grease) are heated, the viscosity of the oil changes. VI is a unitless number that indicates how viscosity changes with temperature change. The lower the VI number, the greater the amount of change in viscosity that occurs when the temperature of an oil changes; conversely, the higher the VI number, the less change in viscosity that occurs when the temperature of an oil changes.

Considering VI’s in the context of the graph opposite makes things more understandable.

In order to assist the reader, we have included some VI brackets of the basic oils we use, including mineral oil:

  • Natural mineral oils range from 80 to 100
  • PAO ranges from 125 to 145
  • Ester ranges from 120 to 150
  • PFPE ranges from 100 to 350
  • Silicone ranges from 300 to 800.

As an example, the viscosity of a mineral oil will alter significantly when the temperature changes; imagine how runny motor oil becomes when the temperature rises. The VI of synthetic oils is greater than that of mineral oils. Diverse Perfluoropolyether(PFPE) oils can have a broad range of potential VI values, and as indicated in the table, siliconeoils have the greatest VI numbers, indicating that they are the oils that change viscosity with the least amount of temperature variation. In most cases, VI is only relevant when comparing one product to another, and when evaluating the usage of a grease, keep in mind that VI refers to the base oil used to manufacture the grease, not the completed grease.

  1. When you look at a data sheet, what does the Viscosity Index look like?
  2. Example 2 of the Viscosity Index (VI): a silicone base oil with a VI of 458.
  3. .how does the apparently arbitrary VI number come to be?.
  4. The equation used to determine VI is VI= 100((L-U)/(L-H)), where L is the oil with a viscosity of zero at 40°C, U is the oil with a viscosity of one at 40°C, and H is the oil with a viscosity of one hundred at forty degrees.

If you’ve made it this far, we recommend that you read the next two items on this page that are related:

  • Understanding Kinematic Viscosity
  • Base oil viscosity demonstration movie
  • Understanding Kinematic Viscosity

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