Why should bearing lubricant viscosity be considered at operating temperature?

LILY Bearing | 2026-10-28

Best answer

Compare viscosity at the condition that matters

Lubricant viscosity changes with temperature, so a value listed at a reference temperature is not a direct statement of the oil's viscosity everywhere in the machine.

Bearing lubricant selection therefore needs the actual operating condition and the manufacturer's applicable method. JTEKT discusses base oil viscosity in relation to speed, load and temperature, rather than using one nominal grade for every duty. A grease's consistency grade cannot supply this missing information either. Keep the viscosity value, its reference temperature and the relevant product data together. Removing the temperature label from the number can make two different descriptions appear falsely comparable.

Use a changed duty to identify what must be recalculated

Suppose the same lubricant is proposed for two similar machines, one operating with a substantially hotter bearing environment.

The matching product label does not show that the oil-film conditions are equivalent. Record speed, load, the relevant temperature evidence and the exact lubricant before applying the manufacturer's selection method. If temperature is estimated, label it as such and state its basis. Do not infer an internal bearing temperature from an unrelated ambient reading. The resulting comparison can identify whether the proposed lubricant has a documented basis for both duties, without inventing a universal viscosity requirement or treating a reference-temperature number as an operating measurement.