Different cooling structures for cylinder head and block and the corresponding thermal status, thermal dissipation and frictional power dissipation were investigated in this study. In a conventional engine cooling configuration, the coolant flow travels from the block to the head, leading to the coolant temperature of the head being higher than that of block. Furthermore, the over-cooling problem in the block will occur because the cooling system is designed for the cooling requirements of the cylinder head without considering the cooling load of the block. This paper developed a 3D single cylinder model to analyse the influence of coolant flow direction and split structure cooling for the head and block. The analysis indicated that the top-bottom flow cooling structure can effectively reduce the cylinder head thermal load and slightly increase the temperature of the cylinder liner. The combined split and top-bottom cooling structure is proven as the optimal solution with the advantages of lower thermal and frictional power dissipation compared with that of the conventional cooling structure. (C) 2017 Elsevier Ltd. All rights reserved.