BIZOMAT MAKEOS · Engineering
Oil Viscosity at Temperature
What is this oil’s viscosity at the operating temperature?
Kinematic viscosity of a lubricating or hydraulic oil at any temperature from two known points (usually 40 °C and 100 °C) by the ASTM D341 (Walther) relation.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| First known temperature | °C | Temperature of the first data point (40 °C on most data sheets). |
| Viscosity at first temperature | cSt | Kinematic viscosity at T1 from the oil data sheet. |
| Second known temperature | °C | Temperature of the second data point (usually 100 °C). |
| Viscosity at second temperature | cSt | Kinematic viscosity at T2. |
| Operating temperature | °C | Temperature you need the viscosity at. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: First known temperature
- What it is
- The temperature of the first viscosity value you know for the oil, normally the lower of the two values on the oil data sheet.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -60 °C to 300 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter degrees Celsius; the tool converts to kelvin itself.
What this means: Viscosity at first temperature
- What it is
- The kinematic viscosity of the oil measured at the first known temperature, from the oil data sheet.
- Units and format
- Enter a number in cSt: centistokes (kinematic viscosity, 1 cSt = 1 mm²/s). The form accepts 0.5 cSt to 1000000 cSt. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 46 cSt as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use kinematic viscosity in centistokes (mm²/s), not dynamic viscosity in centipoise.
What this means: Second known temperature
- What it is
- The temperature of the second viscosity value you know for the oil, normally the higher data-sheet temperature.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -60 °C to 300 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must differ from the first temperature. Enter degrees Celsius.
What this means: Viscosity at second temperature
- What it is
- The kinematic viscosity of the oil at the second known temperature, from the same data sheet.
- Units and format
- Enter a number in cSt: centistokes (kinematic viscosity, 1 cSt = 1 mm²/s). The form accepts 0.5 cSt to 1000000 cSt. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6.8 cSt as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check you have paired each viscosity with its own temperature.
What this means: Operating temperature
- What it is
- The temperature at which you need the viscosity, such as the bearing, gearbox or hydraulic tank operating temperature.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -60 °C to 300 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher temperature gives a lower viscosity.
- Get it right
- Values between the two known temperatures are interpolated and most reliable; outside them the result is an extrapolation.
Method and formulas
- log₁₀ log₁₀(ν + 0.7) = A − B log₁₀(T), with T in kelvin.
- A and B are fitted through the two known points.
- ν(T) = 10^(10^(A − B log₁₀ T)) − 0.7.
- Example: an oil of 46 cSt at 40 °C and 6.8 cSt at 100 °C has about 20.623 cSt at 60 °C.
Limitations
- Valid for mineral and many synthetic oils in the normal range; not below the pour point.
- Multigrade and polymer-thickened oils can deviate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Find operating viscosity for bearing and gear calculations
- Check hydraulic oil at cold start
- Compare oil grades
Who it is for
- Maintenance engineers
- Reliability engineers
- Maintenance technicians
What you get
- Viscosity at the operating temperature
- Walther constants
Interpreting the result
- Compare with the viscosity your bearings, gears or hydraulic components need at operating temperature.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2329–2337, 2698. Topic reference; no source tables or recommended settings are reproduced.
- ASTM D341 Viscosity–Temperature Charts for Liquid Petroleum Products
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Temperature and the Walther relation
What it covers: Find an oil's viscosity at any temperature from its two data sheet values with the Walther (ASTM D341) relation, judge its sensitivity and limits, and avoid linear interpolation.
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