The expansion-control characteristics of steel inserts in the open-sleeve type of diesel-engine pistons were investigated using holographic interferometry. The holographic measurements were compared with the predictions of a finite-elements model of the piston. Due to the complex internal geometry of the piston and the in-built stresses, certain assumptions were made in the model. The measurements made for a rise from 50°C to 60°C showed the effects of these assumptions. At the 130°C to 140°C range, the steel insert was found to have lost control of the expansion of the aluminum-alloy skirt. This was confirmed by releasing the skirt from the sleeve in the model and repeating the analysis. The study has shown that the holographic technique can provide the true deformation behavior of the piston at different temperatures. The measurements can also be used to improve the accuracy of the model.