The light-emitting diode (LED), a semiconductor optoelectronic device, is increasingly introduced into automotive signaling and lighting applications principally due to its exciting design style and long lifetime. Focusing on automotive contexts, numerous researchers have conducted the thermal optimization concerning structure and material properties in LED automotive lamps to maintain the junction temperature operating within a favorable range. However, these efforts mostly rely on thermal simulations with partly component models and specific boundary conditions, and moreover little temperature tolerance has been given from a whole-lamp-level aspect consisting of the electrical, optical, and mechanical requirements. To qualify the temperature tolerance in the thermal design for LED automotive lamps in in-vehicle environment, in this paper, after a description of the design database, the thermal cost objective function, weighted by the electrical, optical, and mechanical objectives, is defined. Then, the multiphysical 3-D simulation model has been made with whole parts in the LED automotive lamp, calibrated by junction temperatures of the typical modules, and integrated with the built database for a graphic user interface application. Finally the temperature sensitivity analysis based on the integrated platform has been performed to accurately estimate the temperature tolerance of the LED automotive lamp. The suggested methodology and experimental results cast light on balancing between the failure risks and costs in LED automotive lamps in the future cars.