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Viscosity & Viscosity Grades


MotoTribology

Viscosity is a measurement of an oil’s ability to flow. Oils can range from viscosities as thin as water to viscosities as thick as asphalt, so there is quite a large window of possibilities to work with when formulating lubricants. There are two varieties of viscosity in which to measure oil. The first is the kinematic viscosity which is measured by the flowing characteristics of oil. The second is called the dynamic viscosity and is measured by the resistance oil exerts on an object pushing through it. Although dynamic viscosity is used to measure properties in motorcycle lubricants, the kinematic viscosity is the biggest factor in classifying oils for various motorcycle applications.

Kinematic viscosity is the main measurement used to differentiate the Society of Automotive Engineers (SAE) various grades of engine oils and gear oils. This is essentially a measurement of the “thickness” of oil and specific ranges of viscosity correspond to specific SAE viscosity grades. At the time of this writing, the SAE currently has six active viscosity grades (60, 50, 40, 30, 20 and 16) with another two (12 and 8) being set for future implementation.

In addition to the kinematic viscosity requirements for an SAE grade, there is an accompanying high temperature high shear (HTHS) viscosity measurement to go along with each grade. Although its name would suggest otherwise, this is not a measurement of the shearing protection an oil provides but instead the viscosity measured under different conditions than the normal kinematic viscosity that can be likened to how the oil will slide over top of itself as opposed to how it flows.

One last point of the SAE viscosity grades is a pair of low temperature viscosity requirements which are related to the “W” grades or the winter grade of an oil (the W stands for winter, not weight as commonly believed). These two measurements indicate the oil’s ability to be pumped through an orifice (its flow) and its ability to let an object pass through it (its solidity).

SAE-EO-chart.png?w=948

Table 1: SAE J300 Engine Oil Viscosity Specification

Table 1 illustrates the differences between each possible grade of engine oil defined by the SAE. Multigrade oils come with a few rules. The winter grade comes first (for example: 5W-40, 10W-30, 20W-50), any oil that has a multigrade designation needs to meet all of the requirements of both grades indicated, and oil marketers are required to print the highest performance grade that the oil meets on the container of oil. This means that oil companies cannot produce a 10W-50 grade oil and market it as a 20W-50 even though it would technically meet and exceed all of the specifications of a 20W-50 because 10W is higher performance than 20W

Gear and transmission oils follow a similar set of requirements with required ranges of the kinematic viscosity at 100°C and a low temperature viscosity requirement.

SAE-GO-chart.png?w=948

Table 2: SAE J306 Gear & Transmission Oil Viscosity Specification

The two tables presented above are the one and only standard way to classify engine and gear oils in the motorcycle lubricant industry. There are other ways to categorize products for use in industrial applications, but they have no place in these discussions. Oils can either be mono-grade meaning they only claim to meet one viscosity specification (ie. 80W transmission oil and 50 weight engine oil) or they can be multi-grade meaning they meet the specifications for two of the classifications (ie. 5W-40 and 25W-60). The specifications are created so that only one winter grade and one weight can be claimed at any point.

Many believe that the winter grade designates how thick an oil will be, as in thinking a 10W-50 will be thinner than a 20W-50 but this is not true. Remember, the winter grade only correlates to an oils behavior at subzero temperatures. The fact that the two oils are 50 weights says that they need to meet the same viscosity range at high temperature. That being said, the tendency for an oil to have a lower viscosity at low temperature (which is desirable) does tend to also make it seem thinner at room temperature so this is where this myth probably originates, but most people see the oil at ambient temperature as they pour it out of a bottle and not as it pumps through a motor at 100°C so it is an understandable belief. However, this is the fact to take away, any 50 weight engine oil (or 20, 30, 40 or 60) behaves exactly like any other 50 weight engine oil (or 20, 30, 40 or 60 respectively) at the operating temperature of an engine. The lower the “W” grade of an oil, the more thermal stability it generally has which is a desirable property in oils, but it is not a given so I don't recommend assuming one oil is better than another just based on that property.

Viscosity is the most basic property of oil and it is without a doubt the most important feature of any oil. Using the appropriate viscosity oil is the first correct choice to make in selecting any lubricant for use in your machines. The machine manufacturers designed the engine or gearbox to operate with a specific lubricant so things like the oil channels, oil pump and clearances are all specific to the recommended grade of oil. The one and only exception to this is the winter grade. You can always go to a lower “W” grade as long as you maintain the regular grade (ie. you can use a 10W-50 instead of a recommended 20W-50). You can sometimes go to a higher “W” grade as well, but that depends on the application and environment and is only advised when the climate does not approach freezing temperatures.

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      JASO Explained PART 1:
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      Table 1: JASO T903:1998 Clutch Friction Specification

      Table 2: JASO T903:2006 Clutch Friction Specification

      Table 3: JASO T903:2011 Clutch Friction Specification

      Table 4: JASO T903:2016 Clutch Friction Specification
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                                    Table 5: JASO T903:2016 laboratory bench testing requirements. These specifications control the chemical and                                   physical properties of motorcycle specific oils.
      Density – A measurement of mass per given volume
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      Kinematic Viscosity - A measurement indicating a fluids ability to flow. The more viscous oil is, the thicker it is. This is sometimes referred to as low shear viscosity. While the result at 40°C only needs to be reported, the result at 100°C must correlate to the designated SAE viscosity grade on file for the product.
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      High Temp. High Shear Rate Viscosity at 150°C (HTHS) – The high temperature viscosity of an oil in high shear rate conditions.
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      Shear Stability – The resistance for an oil’s molecules to be sheared or reduced. This property relates to viscosity stability.
      Color – I sincerely hope this needs no description
      Elemental Analysis – A quantitative measurement of the concentration of chemical elements in a material. Phosphorus is the only element that is controlled or limited by JASO.
      Infrared Absorption Spectrum Analysis (IR Scan) – A type of scan that identifies chemical bonds.

      Figure 1: Example of an IR scan
             This stuff can be confusing, I know. So if any of it is still unclear to you, feel free to PM any questions.
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          So that is the entire JASO 4-stroke engine oil specification minus the labeling requirements and then all it takes is a deposit of ¥40,000 (approximately $400 USD) to the JALOS bank account to be added to their list and to display a JASO box such as the one below on the back label of an oil.

      Figure 2: JASO registration box for rear labels of motorcycle engine oils.
      Only products that are officially registered with JASO and are included on the JASO filed engine oil list are permitted to display this box on their label. So if you see the box, you should be able to look it up on the list to confirm its registration. You can also find the company that owns each formula and if you read the oil code you can tell exactly what country that product is manufactured in. By looking at digits two, three and four of the oil code, which are specified by a corresponding country code in Appendix 3 (Page 19) of the JASO T903:2011 specification document, you can tell the exact country of origin for every product on the list.

      Figure 3: JASO oil code example.
      Why JASO is Important
      Now you may be asking yourself, is registration really that important? It is true that registration is not required to market a product for 4-stroke motorcycle use, but the fact that a product is registered does give assurance from an independent third party that a product does perform as claimed. There are many many brands and products out there that claim to “meet JASO MA requirements” or they may say “meets JASO performance specifications” or something else along that same line. If there is only a claim and no box, then you simply need to take that company’s word for it that they comply, and if there is no official registration, it is only that company’s promise that they are formulating honestly. The products that claim to meet JASO requirements more than likely do, but there is certainly a higher chance that a company that does not register may not be testing to ensure that performance.
      Registering with JASO does have a downside. It makes it difficult to improve formulas any more frequently than once every few years because of the cost involved for each reformulation, so it can make it difficult to adapt to quickly advancing technologies.
      The JASO specifications give a benchmark for motorcycle specific oils that highlights the performance needs that are different from standard automotive oils. By addressing those differences and working with both motorcycle manufacturers and lubricant manufacturers, JASO continues to update the specification every five years or so to remain in step with the most up-to-date technologies; by keeping up-to-date with the technology advancements always happening, it makes sure that oils are able to advance without risking the loss of their JASO registration simply for trying to improve or do things possibly outside the ordinary to create a uniquely performing product.
      What’s Next?
             The T903:2016 specification was released in April, 2016 and is now implemented. There was an attempt to bring in a new test to quantify gear protection, but there were problems validating the test procedure so it is not planned to go into effect until 2021 now.
             The clutch test was revised to give a more accurate differentiation between the categories. So the updated ranges and test pieces now offer a more precise and useful test.
             As mentioned above, gear pitting is an issue they want to address. It was not able to be implemented in the 2016 specification but it is still of interest for eventual inclusion into the specification.
             The FZG Gear Test was the original test considered to analyze gear pitting performance. Unfortunately the FZG test method proposed for measuring pitting protection has been deemed too unreliable to be standardized. There is a lack of repeatability between laboratories performing the test and the cost of each test was determined to be too costly in the end.
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             Unfortunately before the specification can include a new test, the test must display a strong correlation between facilities and a highly repeatable test method. Different users and laboratories must be able to obtain results within a reasonable margin of error, but until that happens, this new test will not be part of the specification. By 2021, they may have a new procedure developed that can work for this purpose.
      Here are some links to the JALOS website for anyone who would like to review the official documents:
      JASO T903:2016 Specification
      JASO 4T List of Filed 4T Engine Oils