Nanofluids, the suspensions of nano-size powders in ordinary fluids, are of technical interest for their enhanced cooling properties, but their possible erosion-corrosion effects on cooling-system materials are mostly unknown. This paper discusses the rationale for designing and developing a new test-rig with flow-through parallel to the tested surfaces. The instrument conduct-chamber accommodates multiple specimens for simultaneous testing, and controlled fluid speed and temperature. This study shows that the new rig yields measurable surface-modifications from nanofluid action in reasonable test-times. Results are presented for a nanofluid (of 2%-alumina-nanopowder in water) that is recirculated in parallel-flow contact with polished aluminum and copper. Surface modifications are assessed by roughness, weighing of removed-material, and optical-microscopy, and results indicate that nanopowders can lead to patterns of wear, erosion and corrosion that are substantially different than those typically obtained from the base-fluids.