For the last decades, internal combustion engine cooling systems have evolved from simple cooling to thermal management. New legislations set demands for lower exhaust emissions. Higher engine temperatures have shown to reduce fuel consumption. Today’s cooling system layouts have low precision, bringing problems in form of thermal fluctuations due to long circuit periods. On the way to increased precision in an engine’s cooling system, predictive tools for analyzing thermal behavior might play an important role. A simulation model has been improved to give accurate results in simulating a normal drive cycle in cold climate. The model is supposed to be a template for testing new layout concepts.A number of layout concepts have been tested and compared with the current layout by some different methods. It is found that there are possibilities to improve the performance in cooling systems by developing the thermostatic valve, but first a definition of which criterions designate a good cooling system is needed.