Abstract: A hub cap vent plug which is resistant to penetration by water sprayed under high pressure during vehicle washing. The plug includes an axially outer end face portion, sidewall portions adapted to mate in fluid-tight relation with an opening in an associated hub cap, and a small diameter opening terminating at one of its ends in a thin web of the plug material. The plug has a valve cover with an inner surface spaced closely apart from said end face portion, thereby defining a pair of transverse openings. A normally closed valve such as a slit in the web allows pressure and vacuum to vent through the valve.