This study establishes the critical temperature of scuffing for contacts of gears made of AISI 8620 steel alloy, lubricated by Dexron 6 oil. Through thermal mixed elastohydrodynamic lubrication modeling, experimental scuffing failures are simulated to determine the associated maximum surface temperature, which consists of bulk and flash components. This temperature is referred as the limiting/critical temperature of scuffing and is believed to be independent of operating conditions, while vary for different solid material and lubricant pairs. It is found that sump lubricant temperature rise affects surface temperature by contributing to the bulk component. The flash component is largely dictated by asperity interactions within the contact zone, where Hertzian pressure is not an appropriate measure of micro-scale asperity contact loading. The observed scuffing scars are shown to be in good agreement with the high temperature zone predicted by the computational model.