A lubricant for a run-flat tire system includes a water soluble, or water-miscible carrier, a thickener, and a surfactant. The thickener hereof retains its rheological properties and is not subject to permanent thinning shear. The base fluid is, preferably, a water-soluble polyhydroxyl or other polyhydric compound and the thickener is preferably a clay. When admixed with a surfactant and, optionally, a lubricity agent, the lubricant exhibits long term stability and (is resistant to heat buildup.) prevents the buildup of heat in the tire assembly when the tire is in the run flat condition.