Samples of 33% glass filled and unfilled poly(butylene terephthalate) [PBT] and nylon 66 (PA66) were injection molded into bars,which were immersed in common engine and powertrain fluids: antifreeze, motor oil and automatic transmission fluid for 25 days. Fluid uptake was measured at 1, 7, 18, and 25 days by gravimetry. Both PBT samples absorbed 0.2-0.25% antifreeze and 0.05 - 0.10% motor oil and automatic transmission fluid (ATF). Both DSC and DMA analysis showed no disruption of polymer thermal transitions or storage moduli. The glass filled PA66 sample absorbed 2.5% antifreeze and 0.25-0.3% of motor oil and ATF and showed an 80°C reduction in the tan delta maximum on DMA. The unfilled PA66 sample absorbed 7% antifreeze and 0.2-0.3% of motor oil and ATF also showed a tan delta maximum 80°C less than the unexposed control. Creep analysis was conducted on the unfilled nylon sample and compared to a virgin material. The softer antifreeze-exposed sample had the expected higher instantaneous strain; however, it had a much reduced viscoelastic response and less permanent deformation. This behavior was thought to arise from hydrogen bond crosslinking of the chains by the imbibed ethylene glycol.