Abstract: The temperature and flow fields of the cooling fluid of a car-engine,suffering hot/cold shocks during up/down hill driving,were empirically approximated,mathematically modeled and theoretically analyzed in bi-directional fluid-solid coupling method,numerically simulated with CFD software and experimentally evaluated.The simulated result show that the flow-rate of coolant has a major impact,and that an increasing cooling-rate occurs from the 1^st to the 4^th cylinders.The most vulnerable areas,with the largest stress/strain/deformation distributions under the hot/cold impact,were found to exist on the fire-face of cylinder head.The simulated and measured results were in good agreement.Accordingly,the geometry of inter-cylinder cooling water jacket was optimized.The test results show that the optimized car engine significantly increased the resistance against the repeated thermal shocks.