The Coolant plumbing assembly is a system to move heat around the engine. The main purpose of the assembly is to carry away the intense heat generated by the combustion in the engines and other applications include heating parts of the engine for cold weather. The engine runs best at a fairly high temperature. When the engine is cold, components wear out faster, and the engine is less efficient and emits more pollution. So another important job of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the engine at a constant temperature. The coolant plumbing assembly is modeled using Pro-E and the analysis is carried out in Ansys 10.0. The Coolant plumbing system is subjected to different fluctuating temperatures from 260oC to room temperature so, detailed thermal and structural analysis was carried out for designing the system and studied different modifications for proposing the optimum design with reduced deformations and stresses due to thermal loads.