The effect of coolant flow pattern on the metal temperature of the combustion chamber was studied in 1.5L and 1.8L gasoline engines. One of the main important points in the design of the water jacket is the increase of the coolant flow velocity. In this paper, the water jackets of the cylinder head and the cylinder block were visualized for the purpose of improving the coolant flow pattern. By the use of this technique, the optimal design of the size and th location of the water transfer fole was possible. And, to lower the metal temperatures of the thermally critical parts, the drilled water passages were employed. To investigate of effect of the improved flow pattern and the drilled water passages, the metal temperatures of the combustion chamber were measured. As a result of the temperature measurement, it was found out that both the change of flow pattern and the drilled water passages have significant effect on the reduction of the peak metal temperature.