KEVOS® MAKEOS · Power Transmission
Gearbox Oil Temperature and Grade Check (Heat Balance, Viscosity Hot)
At what temperature will my gearbox oil settle, does it need a cooler, and is the oil grade still thick enough at that temperature?
Check of a gearbox’s steady oil temperature and its lubricant: heat generated from the power and efficiency, the equilibrium oil temperature from the housing’s dissipation, the thermal power limit, cooler duty and oil flow if needed (as the gearbox heat balance tool), and the oil’s viscosity at the running temperature (the equilibrium temperature, or the limit if a cooler holds it there) from its viscosity at 40 °C and 100 °C (as the oil viscosity–temperature tool), against the least viscosity the gears need.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Input power | kW | Power going into the gearbox. |
| Gearbox efficiency | % | Overall efficiency of the gearbox. |
| Heat-dissipating surface area | m² | Outside surface area of the housing that sheds heat. |
| Heat transfer coefficient | W/m²·K | Combined convection and radiation coefficient of the housing (higher with a shaft fan). |
| Ambient temperature | °C | Air temperature around the gearbox. |
| Maximum oil temperature | °C | Highest oil temperature you allow. |
| Oil temperature drop across a cooler | K | Temperature drop of oil through a cooler, if one is needed. |
| Oil specific heat | kJ/kg·K | Specific heat of the oil. |
| Oil density | kg/m³ | Density of the oil. |
| Oil grade | ||
| Viscosity at 40 °C | cSt | Kinematic viscosity of the oil at 40 °C (from the data sheet). |
| Viscosity at 100 °C | cSt | Kinematic viscosity at 100 °C. |
| Least viscosity the gears need at running temperature | cSt | Least viscosity the gear maker requires at the running temperature. |
Method and formulas
- Heat = P (1 − η); equilibrium temperature = ambient + heat ÷ (h A); thermal limit, cooler duty and flow (as the gearbox heat balance tool).
- Running temperature = equilibrium temperature, or the maximum if a cooler is fitted to hold it there.
- Viscosity at the running temperature by the ASTM D341 relation through the 40 °C and 100 °C values (as the oil viscosity–temperature tool).
- Example: the oil settles at 70 °C where the oil is 51.702 cSt against 50 cSt needed.
Limitations
- Steady state; start-up and intermittent duty run cooler.
- Single housing coefficient; sun, enclosures and nearby heat sources change it.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a gearbox for a higher power or hotter site
- Choose an oil grade for the running temperature
- Decide whether a gearbox needs a cooler
Who it is for
- Maintenance engineers
- Lubrication engineers
- Design engineers
What you get
- Heat generated and equilibrium temperature
- Thermal limit, cooler duty and oil flow
- Viscosity at the running temperature
Interpreting the result
- A shaft-mounted fan can double the housing coefficient, often removing the need for a cooler.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3339–3340, 2430–2436, 2329–2337. 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 Gearbox Oil Temperature and Grade Check (Heat Balance, Viscosity Hot) calculator
