The exhaust manifold is one of the engine components which is used to collect the burned gases from the cylinder head and send it to the exhaust hot end aftertreatment system with low engine backpressure. The main purpose of the automotive exhaust manifolds are providing a smooth flow field and must be able to endure thermo-mechanical loadings. The present paper explains the CAE analysis method to assess the design of exhaust manifold of a heavy duty diesel engine. Coupled computational fluid dynamics (CFD) analyses were performed to solve the flow field within the exhaust system and surface convection loading prediction at fluid side and obtain temperature distribution at solid region of exhaust manifold domain. The metal temperature prediction provided by thermal model is used to carry out the durability analysis of the structure. A transient nonlinear Finite Element Analysis (FEA) is undertaken to simulate the inelastic deformation and predict thermo-mechanical fatigue (TMF) failure. Gasket sealing prediction is another analysis concern which is driven by FEA in exhaust manifolds since any gas leakage affects the engine performance.The use of such CAE approach allows the design and analyses engineers to diagnose critical locations or to find the root cause of manifold failures in an early stage of development and to meet measures in order to remove local structural weaknesses. This minimizes the need for expensive hardware testing, also reducing the overall product development cycle time and cost.