Automotive vehicle includes various systems like engine, transmission, exhaust, air intake, cooling and many more systems. No doubt the performance of individual system depends upon their core design. But for performance, the system needs to be fastened properly. In automotive, most of the joints used fasteners which helps in serviceability of the components. There are more than thousands of fasteners used in the vehicle. At various locations, we found issue of bolt loosening and because of this the design intent performance is not met by the system. During product development of ECS (Engine cooling system), various issues reported to loosening the bolt. The pre-mature failure of bolt loosening, increases the interest in young engineers for understanding the behavior of fastener in vehicle running conditions. This paper focuses on the design of wedge shape of washer to avoid bolt loosening. Further, the paper is reinforced with FEA simulation for understanding the behavior of the bolt loosening. The joint in ECS is tested experimentally and FE simulated using simulation tools with various methods under different vibration conditions like normal nut, with washer, with spring washer, with check nut and wedge washer. The results of the wedge washer are extremely encouraging and proves that this type of design could be cost effective and can eliminate the issue of bolt loosening at one go. This solution could be extremely easy to implement in field vehicle also, as there are no major changes in the system.