General Information
As a function of their design, hubcap vent plugs will on occasion exhibit signs of hub oil on their exterior surface. Depending on environmental conditions and/or age of the plug, the amount of oil present can vary. This is a normal result of the venting process due to pressure increase within the hub cavity. For an example of normal vent plug appearance, see Fig..
Fig. 1, Normal Oil Venting
A vent plug can wear or be damaged and cause excessive leakage, or allow water to enter the hub and contaminate the oil. For examples of a leaking vent plug, see Fig. and Fig.. Evidence of a leaking vent plug may appear as;
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Oil splatter around the wheel.
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Gooey/gummy oil around the vent plug purge point.
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Hub/plug area is dirty, and water contaminated oil in the hub.
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Hub/plug area is clean, but there is water contaminated oil in the hub. (pressure washing is the most likely cause)
Fig. 2, Excessive Leakage
