Research about learning styles show that many engineering students are visually inclined. Therefore, we study engineering students' use of visualizations to communicate while solving mathematical problems. Based on a framework for mathematical representations, visualizations and mediation, we set up an explorative study with the visualization tool Sim2Bil, which combines a simulation of two cars, velocity graphs, and an input for velocity functions. We asked three engineering students to create a simulation for the cars with certain conditions and studied their visualizations related to verbal, graphical and symbolical representations. The visualizations were Sim2Bil-based, paper-based and gestures and these were all used in different stages of the problem solving.