Compare the temperature with the machine baseline, bearing type and measured operating condition. Common causes include excess or insufficient grease, contamination, misalignment, excessive load and incorrect mounting. Review evidence before deciding on the repair.
What the symptoms may mean
These observations help organize the investigation. They do not prove the root cause.
| Observation | Possible cause | Useful evidence |
|---|---|---|
| Temperature rises after greasing | Excess grease, wrong grease or mixing of incompatible products | Greasing quantity, product and service record |
| Heat rises with load or speed | Increased bearing load, misalignment or application limits | Load and speed trend |
| Heat with rumbling or vibration | Lubrication breakdown, damage or contamination | Vibration and bearing inspection history |
| One bearing runs hotter than before | Changed mounting, axial load or local cooling | Temperature locations and overhaul record |
Understanding the possible causes
Lubrication must suit the bearing
Too little lubricant can reduce the separating film between rolling surfaces. Too much grease can increase churning and temperature, especially soon after servicing. Grease selection, intervals and quantities depend on the exact bearing and motor design.
Alignment and loading influence temperature
Coupling misalignment, belt tension, incorrect fits and excessive axial load may put additional stress on a bearing. A failed bearing may be the result, not the first cause. The driven machine and mounting condition are part of the diagnosis.
Use a consistent temperature trend
A surface infrared reading is influenced by measurement location, emissivity and ambient temperature. Comparing different points or measurement methods without recording the conditions can be misleading. Combine temperature trend with vibration and operating records.
Bearing type and motor design matter
Some motors use insulated bearings or special arrangements for inverter duty. The appropriate investigation depends on shaft size, bearing arrangement, speed and drive system. Replacement specifications should come from the OEM and maintenance plan.
Questions to narrow the problem
Collect existing operating records first. Inspection or electrical testing requires a qualified person and appropriate authorization.
- When was the bearing last lubricated and with which product?
- Did the trend change after overhaul, belt adjustment or coupling work?
- Is the temperature measured at the same position and operating load each time?
- Is there unusual noise or a change in vibration?
- What is the exact bearing identification and motor duty?
What to do next
Record the temperature trend, vibration, lubrication history and load. A competent maintenance team should assess the urgency and approved isolation-based inspection before any bearing work.
Common questions
Does a hot bearing always need replacement?
No. Lubrication, load, misalignment or measurement effects may explain the change. Confirm the cause first.
Can adding more grease solve overheating?
Not necessarily. Excess grease can also raise temperature. Follow the approved lubrication specification.
Technical references
The linked sources explain general fault principles. The site-approved equipment manual and protection design take precedence.
- SKF: Rolling bearings and seals in electric motors and generators
- SKF: Bearing damage and failure analysis
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Electrical Doctor helps organize symptoms and prepare preliminary case notes. It does not authorize repair or switching work.
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