This paper describes the use of a large-scale, multi-semester design project as a means of integrating six courses in the mechanical engineering curriculum. The project, a bench-scale hybrid powertrain, is built up -- component by component -- as students advance through the curriculum. The authors used the project to test two research hypotheses: (1) that a long-term, large-scale design project would increase long-term subject matter retention and (2) that a long-term, large-scale design project would increase students' design and problem-solving skills. The authors found that the design project had no measurable effect on long-term subject matter retention, but did have an impact on design thinking and skill. The paper gives a full description of the project and assessment effort, and provides some of the insights acquired by the authors while conducting this research. A complete description of the project and videos of student designs can be found on the project website, www.benchtophybrid.com.