This paper investigates the way of improving the mixing of highly viscous Newtonian fluids in a tank using suitable operating conditions (unsteady stirring approaches). The agitator used is a non standard helical ribbon impeller fitted with an anchor at the bottom. The degree of homogeneity in the tank is followed using a conductivity method after a tracer injection. It is shown that the use of time-dependent rotational speed during the mixing process allows energy savings. For the unsteady stirring approaches tested, energy savings can reach up to 60% compared to the energy required to obtain the same mixing time with constant impeller rotational speed. Finally, a model is provided which allows the prediction of the mixing process of the agitated system with Newtonian fluids for both steady and unsteady stirring approaches.