A wellbore tool is conditioned between downhole deployments with a substantially continuous application of a conditioning fluid within the tool. Selectively removable caps connect to ends of the tool after its removal from the wellbore. If the tool is part of a downhole string, the caps are added after the tool is decoupled from the remainder of the string. The conditioning fluid is introduced into the tool through a fitting on one of the end caps; and while a fitting on the other end cap is opened to vent fluids resident within the tool. The caps are in sealing contact with a housing of the tool to retain the conditioning fluid inside the tool. A fluid supply system at the well site provides the conditioning fluid. Example conditioning fluids include a fracturing fluid, a completion fluid, a diluent, a solubilizing agent, an anti-scaling agent, a pH buffer, a liquid freezing point depressant, corrosion and oxidation inhibitors, oxygen scavengers, biocides, surfactants, and combinations thereof.