:The market for composite engine oil sealing components, such as valve covers and oil pans, continues to expand, replacing traditional metal stamping and die casting materials. As the market for these composite components grows, so must the understanding of the material performance characteristics and the relationship of these characteristics to the design of the part. Unlike metals, composites are viscoelastic in nature, exhibiting time-temperature dependant properties. Therefore, the traditional design approach utilizing static property data to predict long-term performance under load and over a wide temperature range will not sufficiently characterize the nonlinear property response of polymeric-based composites. A robust composite sealing design requires complete materials characterization, including long-term creep performance as a function of temperature, loading, and cycling.During the product development stage of an engine sealing system, the use of finite element techniques is a viable approach to modeling component performance. Dynamic, long-term material performance data is critical in this modeling, because the available sealing force begins to change as the materials creep and relax, thus directly impacting the sealing ability of the system. This paper will present the creep performance of various thermoset composite materials and show how this information can be used to provide essential design criteria to generate targeted sealing force for the under-the-hood component.