Increasing the operating temperature of automotive proton exchange membrane (PEM) fuel cells above 100^◦C is essential to reducing cooling system complexity yet might lead to a reduced fuel cell lifetime simultaneously. This work aims to establish a fundamental understanding of the various localized effects at elevated temperatures and its correlation with fuel cell lifetime. Therefore, a predevelopment automotive fuel cell at industrial scale was operated in a realistic operation window for 500 h while fuel cell degradation was examined based on four methods: (1) spatially resolved current density, (2) cyclic voltammetry measurements, (3) electrochemical impedance spectroscopy, as well as (4) an extensive post-mortem analysis. The examination led to three findings: Firstly, during operation above 100^◦C, the highest current densities were observed in the crossflow region of the humidified inlet gas streams whereof a minimum in the anode outlet tentatively is assigned to localized membrane drying. Secondly, after 500 h of operation, the fuel cell suffered from severe power density loss (~45 %) attributed to a partial flooding and localized H₂ starvation in the anode outlet region. Thirdly, contrary to presumptions, NMR spectroscopy did not reveal a change in the chemical structure of the perfluorosulfonic acid (PFSA) membrane. This unexpected finding allows assuming that chemical degradation is not critical for automotive fuel cells under realistic operating conditions. Ultimately, the results are key for designing improved flow field designs and innovative ionomer materials for automotive PEM fuel cells operated at high temperatures.