Polyphenylene sulfide (PPS) molding compounds are unique engineering thermoplastic materials which exhibit a very advantageous combination of properties for use in automotive underhood applications. These characteristics include outstanding chemical resistance, good mechanical properties at elevated temperatures, precision moldability, and excellent dimensional stability in the underhood environment.The current situation with regard to oil price has created renewed emphasis within the automotive industry on improving fuel economy. One approach to this is to reduce the overall weight of the automobile, particularly in underhood engine components. Due to the unique engineering characteristics of polyphenylene sulfide compounds, they can be used very economically in some of these applications, and result in weight savings of 25% to 80%, just on the basis of a lower density. Candidate applications include fuel systems, integrated induction systems, camshafts, coolant system components, transmission components and many others.Designing successfully with glass reinforced thermoplastic compounds, however, requires consideration of factors which would not normally be considered when designing with metal. This paper will discuss the design considerations necessary for designing this type of component for the use of fiberglass reinforced engineering thermoplastics. These considerations include: The effect of glass fiber alignment on strength Properties at elevated temperature Effect of aging at elevated temperature Effect of chemical exposure Elevated temperature weld line strengthThe paper will also provide property values of polyphenylene sulfide compounds for design purposes with consideration of each of the mentioned effects, and guidelines for consideration of combined effects.