Abstract: A method of determining the location and type of dimensional defects, particularly friction generating defects, which comprises: (a) initiating simulated operation at ambient conditions of an assembly having certain sliding or rolling contact surfaces; (b) sensing any change in the temperature of such assembly surrounding each certain sliding or rolling contact surfaces (i) with a resolution of 0.02-1.0 C.degree. (preferably 0.1-0.7 C.degree.) and (ii) during a time span of 2-10 seconds measured from such initiation to provide separated voltage signals for each location; (c) converting the signals to a digitized thermal map; and (d) comparing the sensed digitized thermal map with a reference digitized thermal map for such an assembly without defects operated during the same time span and adjusted to compensate for any differing thermal conditions. Any deviations detected by such comparison representing defects.