KEVOS® MAKEOS · Maintenance
Lubricant Viscosity Check (Operating and Cold-Start Viscosity)
Is this oil grade thick enough at the operating temperature and thin enough to circulate at a cold start?
Check of an oil grade for a bearing, gearbox or hydraulic system: viscosity at the operating temperature and at the cold-start temperature from the oil’s viscosity at two temperatures by the ASTM D341 chart relation (as the oil viscosity–temperature tool), the same values in dynamic viscosity and Saybolt units (as the viscosity units tool), and the ratio of the operating viscosity to the minimum your machine needs, against your cold-start limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| First data temperature | °C | Temperature of the first viscosity value on the oil data sheet (usually 40 °C). |
| Viscosity at the first temperature | cSt | Kinematic viscosity at the first temperature. |
| Second data temperature | °C | Temperature of the second value (usually 100 °C). |
| Viscosity at the second temperature | cSt | Kinematic viscosity at the second temperature. |
| Oil specific gravity | Specific gravity of the oil (for dynamic viscosity). | |
| Machine | ||
| Operating temperature | °C | Steady operating temperature of the oil in the machine. |
| Least viscosity needed at operating temperature | cSt | Least viscosity the bearings, gears or pump need (from the component maker or a film thickness calculation). |
| Cold-start temperature | °C | Lowest temperature at which the machine starts. |
| Largest viscosity for a cold start | cSt | Highest viscosity the pump or system can start with (from the pump or system maker). |
Method and formulas
- log log(ν + 0.7) = A − B log T (T in kelvin) through the two data points (as the oil viscosity–temperature tool).
- Dynamic viscosity = ν × specific gravity; SUS ≈ 4.632 ν (as the viscosity units tool).
- Viscosity ratio = ν at operating ÷ least needed; cold-start viscosity against the limit.
- Example: at 70 °C the oil is 19.966 cSt (ratio 1.3311); at 5 °C it is 678.2 cSt.
Limitations
- Straight-grade mineral and synthetic oils; viscosity-modified oils may shear thin.
- Extrapolating far beyond the two data temperatures loses accuracy.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check an oil grade for a machine running hotter than planned
- Choose a grade for a cold climate
- Compare two grades for a gearbox
Who it is for
- Maintenance engineers
- Lubrication technicians
- Reliability engineers
What you get
- Viscosity at operating and cold-start temperatures
- Dynamic and Saybolt equivalents
- Viscosity ratio and checks
Interpreting the result
- If neither limit can be met by one grade, the machine needs oil heating, cooling or a higher-index oil.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2329–2337, 2425–2426. Topic reference; no source tables or recommended settings are reproduced.
- ASTM D341 Viscosity–Temperature Charts for Liquid Petroleum Products
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Lubricant Viscosity Check (Operating and Cold-Start Viscosity) calculator
