Bearing temperature generally rises with start-up and stabilizes at a temperature slightly lower than at start-up (normally 10 to 40 °Chigher than room temperature) in a certain time. The time before stabilizing depends on the size, type, speed, and lubrication system of the bearing and the heat dissipation condition around the bearing. It ranges from about 20 minutes to as long as several hours.

If bearing temperature does not stabilize but continues to rise, the causes shown in Table 1 are conceivable Operation should be stopped and an appropriate corrective action should be taken.

High bearing temperature is not desirable in view of maintaining an adequate service life and preventing lubricant deterioration. A desirable bearing temperature is generally below 100 °C.

Table 1: Major causes of high bearing temperature
(1) Extremely insufficient or excessive lubricant
(2) Poor installation of the bearings
(3) Extremely small bearing clearance or extremely heavy load
(4) Extremely high friction between lip and seal groove
(5) Improper lubricant type
(6) Creep between the fitting surfaces