Can bearing heat discolouration be used to calculate the exact operating temperature?

LILY Bearing | 2026-10-28

Best answer

Keep colour evidence within its actual limits

NSK's discolouration guidance discusses surface colour changes in connection with several operating and lubricant conditions.

The appearance depends on more than a single known temperature, so a photograph cannot automatically be converted into a precise operating-temperature history. Lighting, surface deposits and the condition of the examined component can further affect the observation. Record the colour and its location, but distinguish that description from a measured temperature or a proven overheating mechanism. The absence of a recorded temperature should remain a missing fact, not be replaced by a confident number inferred from a colour chart of uncertain applicability.

NSK: Discoloration

Compare the observation with recorded operating evidence

Preserve photographs under identifiable conditions and note whether the surface was cleaned before examination.

Gather the actual temperature readings, sensor locations, load and speed history, lubricant information and any event records available. If no temperature data exist, ask what further examination can support the suspected mechanism rather than assigning an exact peak. A report might correctly state “discolouration observed on the cage guide surface” while leaving the temperature and cause unresolved. That is more useful than an invented thermal history because it keeps the distinction between observation and interpretation clear for the specialist reviewing the specimen and the proposed corrective action.