If the operating temp is much over 150 F, then special seals and grease and cage materials and internal clearances may be necessary. High operating temperatures may unavoidably result from bearings in hot environments or processes.
Even if the main source of bearing temperature is heat generated by the bearing itself, sometimes the danger does not come from the operating temperature. Instead an internal problem, or inadequate or excessive lubrication, abuse or a mis-application will cause the bearing to FAIL at a relatively low housing temp. But with luck there will be a symptom of a (too) rapid temperature increase.
I have witnessed a few machine tool spindles whose bearings failed CATasrophically before the housing internal temperatures reached 130 F very close to the bearing outer races. But, the temps were climbing at 5 or 10 degrees/minute. (Yes, the temp deep within the bearing was much higher at the time of death). It was not the temperature, or even the temp rise itself that was the problem. The temp rise was merely the symptom of a problem, and resulted from the thermally induced increase in internal preload generating plenty of heat.
If we expect to keep our spindles from failing during development or operation we have to monitor rate of temp increase AND absolute temperature.
