The Automotive thermoplastic industry has seen the introduction of Long Glass Fiber (LGF) composites during the past several years, offering specific performance advantages over short glass fiber thermoplastic grades. The need to develop stronger, lightweight, and cost-competitive materials is critical for the industry in meeting C.A.F.E. requirements of the future. The intent of this paper is to supply design engineers with long term performance data for several LGF thermoplastics at various elevated temperatures, shown in comparison to short glass fiber (SGF) composites. The study will evaluate long-term tensile property performance at 200° F, 275° F, and 300° F. At these temperatures, advantages should be realized over SGF composites when using LGF polypropylene, nylon 6/6, and polyphthalamide (PPA) thermoplastic composites, respectively.The mechanical enhancements of LGF composites realized at room temperature over short fiber competition are; improved impact, tensile, flexural, and fatigue/creep properties. These unique characteristics allow only LGF composites to replace even metals in demanding Automotive under-the-hood, under-carriage, and interior support applications. The presentation of the data from this paper will provide evidence that LGF composites offer performance advantages for these particular applications, which most definitely require excellent mechanical property performance at elevated temperatures.Tensile data for each temperature will be separated into two categories; high performance grades (LGF nylon & PPA vs. SGF) and medium performance grades (LGF PP vs. SGF polyacetal). Current day economic considerations (material cost) were also considered in defining this method of grouping.The scope of the paper will include oven-aging data up to 4,000 hours at each temperature; 200° F, 275° F, and 300° F. Data collected will include tensile strength, tensile elongation, and tensile modulus and will be presented in both graphical and tabular format.It is expected that the LGF composites will offer performance advantages over SGF composite alternatives at each given temperature environment. Specific benefits at elevated temperature should be seen with using PPA type composites (LGF or SGF) over other glass fiber reinforced thermoplastic composites.