Engineering thermoplastics are being used increasingly in automotive exterior body applications; most of these applications require that the panels be painted “on line” with the rest of the car body at relatively high temperatures. The high temperatures associated with the painting/conditioning of the car have been shown to cause dimensional stability problems on automotive fenders molded from NORYL GTX®. This paper contains the results of an extensive FEA investigation targeted at determining what factors cause dimensional problems in fenders exposed to high heat. The ABAQUS FEA software was used to perform computer simulations of the process and the C-PACK/W software was used to determine molded in stress values. The results show that there are primarily three factors which lead to poor dimensional stability of GTX fenders, the thermoplastics high temperature visco-elastic properties (creep), the post mold shrinkage of the thermoplastic and the molded-in stress created by the high pressure injection molding process.