The hubcap is constantly exposed to hot, cold, wet, dry and abrasive conditions, but would you believe that some of the toughest treatment comes from inside the wheel end assembly? There are many factors that lead to damaging conditions such as an over-tight bearing or cocked seal, but one of the most critical issues that can lead to a cooked hubcap is improper lubricant.

Don’t know about improper lubricant? Very simply, there are two types of lubricants that today’s truck and trailer manufacturers pre-determine for their wheel end assemblies — grease or oil. Similar to the expression, “Oil and water don’t mix,” you should never mix grease and oil lubricants in the same assembly. Mixing the different lubricants in the same assembly will inevitably result in wheel end failure. Here are a few indicators of hubcap failure due to improper lubricant:

Milky window: The view window in the hubcap will become nearly opaque white when subject to heat. The heat comes from inside and spells trouble. Pull the wheel and check the bearing adjustment to check for low lubricant or a change to an incompatible lubricant.

Melted window: With the hubcap removed, inspect the edges of the view window for damage or discoloration. If the edge has a rippled look, chances are it has started to melt from excessive heat. Heat build-up could be from running on low lube, excessive pre-load on bearing or a recent switch to an incompatible lubricant.

If either condition occurs, clean all lubricant out of the hub, and then clean and inspect bearings for damage. To avoid this common problem, SKF recommends always checking for the proper lubricant prior to re-installation.