This study reports on an investigation to determine the root cause of engine failures that occurred when engines were run on low sulfur diesel fuel and a high ash SAE 40 API CD quality synthetic oil. Four WARTSILA SACM DIESEL 4-stoke UD45 V16 engines being used in a power generation application experienced high blowby at relatively low engine hours. In addition filters were plugging in less than 30 hours of operation. Borescope inspection of the engines revealed heavy deposits on the top of the pistons and scuffed cylinder liners. Upon disassembly stuck rings were found with heavy deposits also present on the ring lands and inside the top and second ring grooves. A thorough analysis of the engine operating conditions and engine design revealed nothing that would have contributed to the engine failures. Oil analysis showed no unusual trends other than a slight but consistent increase in calcium content. Laboratory testing was done to confirm a hypothesis that the oil selection had contributed to an incompatibility in this application. After replacing the liners pistons were cleaned and installed with new piston rings. With a nominal 1% ash 15W-40 API CG-4 mineral based oil installed the engines were successfully commissioned.