Would it be possible for an additively manufactured impeller of fused deposition modeling (FDM) technology to have a functional behavior and a similar performance to that of the original impeller of a close-coupled centrifugal pump? In this research paper, different tests are conducted to answer this question and to evaluate the manufacturing process of FDM functional parts. Three performance experiments with the same centrifugal pump, using an open test rig, are carried out and compared, first using the original impeller provided by the manufacturer of the pump, second using an FDM replication of the original one without post-treatment, and third using a chemically dimethyl ketone post-treated FDM replication. The results obtained in the tests demonstrate the functional behavior of both additive FDM impellers in comparison with the one fabricated by means of conventional technology (subtractive manufacturing). Additionally, analogous head-flow curves (and also with an improved performance to the one of the original impeller) are obtained. This research paper introduces significant information concerning a low-cost and low-time manufacturing process of additive functional parts. Moreover, new results are presented regarding the performance of chemically post-treated FDM parts working in functional applications. FDM impellers of high complexity and quality, which meet performance criteria, can be achieved.