The normal operating temperature of hubcap grease or oil should not get above 225°F (107°C), notes Spectra. Dana and Meritor both recommend that when the temperature reaches 250°F (121°C) you'd better do a more detailed wheel-end inspection. The Hub Alert label will indicate the need for that deeper inspection of the overheating wheel end.
Catching bearing and seal issues early will reduce the need for over-the-road emergency repairs and will avoid additional and costly repairs due to a failure. Might prevent a fire, for that matter, and could even save a life or two. Wheel-off incidents haven't disappeared, after all.
The Hub Alert thermo-sensitive area is hermetically sealed against moisture, oil, grease, fuels, solvents, water and steam. The sensor decal will turn black once the hub/hubcap surface has reached the critical temperature. Maintenance staff and drivers are thus alerted to the need for inspection. A new heat-sensing label is applied once the issue has been resolved.
More info: www.spectraproducts.ca