Causes, Symptoms and Handling of SKF Abnormally High Operating Temperature

SKF bearings are widely recognized for their reliability, yet under certain conditions they can run unexpectedly hot. Recognizing the root causes, early symptoms and correct remedies is essential to prevent costly downtime and irreversible bearing damage.

1. Bearing Cooling Circuit Failure

Interruption or insufficient flow of cooling water is one of the most frequent triggers. A blocked heat-exchanger, collapsed hose or closed valve reduces heat dissipation, allowing the bearing outer ring to act as a heat sink that quickly surpasses 90 °C. Operators should first verify coolant level, pump pressure and the integrity of all hoses; any debris must be back-flushed immediately .

2. Bearing Lubrication Degradation

Oil that has oxidized or become contaminated with moisture or solids loses its film strength. Metal-to-metal contact then raises the raceway temperature within minutes. Check the reservoir for colour change, sludge or metallic particles; send an oil sample for ISO 4406 analysis if doubt exists. Replace the charge with the grade recommended by SKF, and be sure the new fill quantity respects the “min–max” sight-glass limits .

3. Bearing Over-load or Pre-load

Axial or radial loads beyond the catalogue rating force the rolling elements to skid instead of roll, generating frictional heat. Verify the equivalent dynamic load P against the basic rating C; if P exceeds 0.12 C continuously, consider re-sizing or adding a second support bearing. Equally, excessive pre-load from over-tightened lock-nuts or shrunk fits can raise the internal clearance into negative territory—measure axial displacement with a dial indicator and back the nut off to SKF’s prescribed position .

4. Bearing Misalignment and Seal Rub

A few tenths of a millimetre of angular misalignment can load only one row of rollers, producing localised hot spots. Laser-align the shaft to within 0.05 mm/m. Likewise, contacting seals that are cocked or over-tightened create a frictional brake; run a finger along the seal lip after shutdown—if it feels “tacky” or shows a blue tint, realign or replace the seal with a lower-spring-tension design .

5. Typical Symptoms Shown by the Bearing

• Digital thermometer alarms above 80 °C for greased units or 70 °C for oil-bath designs.
• Discolouration of rings or rollers to straw-blue, indicating tempering.
• Audible pitch change—whine above 3 kHz or intermittent “clicks.”
• Vibration spectrum peaks at BPFO/BPFI harmonics when analysed by accelerometer.

6. Step-by-Step Remedial Action

1. Shut the machine down under controlled conditions; never quench the housing with water.
2. Lock-out/tag-out, then measure shaft run-out and housing bore roundness—remachine if out of tolerance.
3. Flush the cooling circuit with a 2 % citric-acid solution, followed by demineralised water until pH neutral.
4. Drain all old lubricant, clean the chamber with lint-free cloths and refill with fresh ISO-VG 68 or 100 as specified.
5. Re-install the bearing using induction heating to 90 °C max; drive it up the shaft with a silicon-bronze drift to avoid brinelling.
6. Re-commission at 50 % load for 30 min, logging temperature every 5 min; only return to full load when T stabilises within 55 °C ± 5 °C.

By systematically addressing cooling, lubrication, loading and alignment, most overheating events can be resolved on the spot and bearing life restored to its design expectation.

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