In this paper, the flow patterns and velocity distributions of coolant flow around cylinder liners of diesel engine are studied by numerical calculation and experimental observation. The experiment is carried out by oil film method and direct observation with a transparent acrylic cylinder liner. The calculation is performed with the 3-dimensional model by FEM for fluid flow.The motion of coolant flow by calculation corresponds with the result by oil film method and direct observation with transparent cylinder liner. The visualization of the 3-dimensional calculation gives a good understanding about motion of coolant flow and pressure distribution in water chamber.This method is applied to improve the coolant flow with the stagnation around cylinder liner. The effect of improved design is confirmed by experiment. That is, there are no stagnations in the flow around cylinder liners.In addition to the experimental method the numerical calculation for fluid flow is effective and practical for solving the coolant flow problems in engines.