Tests were performed to evaluate the performance of high oleic soybean oil-based hydraulic fluids in long-duration pump tests. Formulations for a conventional hydraulic fluid and a food grade fluid were operated in a low volume hydraulic system for up to 1000 hours. Traditional measures of fluid performance including pump wear, total acid number and viscosity change indicate overall acceptable fluid performance. In addition, a methodology for studying the time-dependent change in pump cartridge surface roughness was investigated. Results indicate that changes in pump roughness correlate with changes in other traditional measures of fluid performance and this additional wear parameter could be useful in developing models to better understand the time-dependent behavior of the system and thus to guide efficient development of enhancements to the oil-additive package.