Thermo-structural behavior of two cast iron commercial exhaust manifolds is investigated through transient nonlinear finite element analysis (FEA). Two different FE models are presented. The first FE model considers interaction between exhaust manifold, gasket and cylinder head. It also considers fasteners initial pretension and geometric constraint conditions. The second FE model only considers the exhaust manifold. Thermal exchange interfaces are evaluated and thermal analyses are conducted to evaluate thermal distribution and to obtain thermal inputs for structural analysis. FE models are solved for stress-strain estimation. Numerical results are validated with experimental data.