A reduction in CO2 emissions and consequently fuel consumption is essential in the context of future greenhouse gas limits. With respect to the thermodynamic loss analysis of an internal combustion engine, a gap between the net indicated thermal efficiency and the brake thermal efficiency is recognizable. This share is caused by friction losses, which are the focus of this research project. The parasitic loss reduction potential by replacing the mechanical water pump with an electric coolant pump is discussed in the course of this work. This is not a novel approach in light duty vehicles, whereas in commercial vehicles a rigid drive of all auxiliaries is standard. Taking into account an implementation of a 48-V power system in the short or medium term, an electrification of auxiliary components becomes feasible. The application of electric coolant pumps on an Euro VI certified 6-cylinder in-line heavy-duty diesel engine regarding fuel economy was thus performed. The engine has two cooling circuits, one low temperature circuit for the charge air coolers and one high temperature circuit as main circuit, which are split in two separate circuits. This layout provides the opportunity to determine the charge air temperature level on demand, which may on the one hand be used for lower NOx emissions, or on the other hand enable exhaust gas heating. Moreover, an operating strategy with respect to a reduced coolant flow rate is investigated and the advantages in the brake thermal efficiency are determined. Future emission tests will include real driving and cold-start phases also for heavy-duty application, where an optimized thermal management will play a key role. The influence of the modified cooling system layout on the warm-up in the worldwide heavy-duty transient cycle is thus presented. Furthermore, the additional degree of freedom offers the possibility to run the pump after the engine is turned off. This post-run phase and its benefits on component protection will also be presented.