Coating system optimization is a critical step in the design and development of plasma-sprayed thermal barrier coatings (TBC’s) for diesel engines. Physical and mechanical property measurements and bench screening tests were performed to evaluate the candidate TBC systems. Additional understanding of the material behavior and failure mechanisms of thick TBC’s gained from the property measurements and bench testing was identified. A specific graded zirconia (ZrO2)/bond (NiCrAlY) coating material system with good strain tolerance and fatigue resistance was selected for follow-on diesel engine durability testing.