I feel like making a differentiation between the putrid smell of decomposition and the "smell of death". In an acutely ill person you can smell the smell of death while a person is still alive but the body has started the process of shutting down. Ask any nurse. After death there is an odor, the smell of death. It intensifies with time and I can only imagine with heat. Even if you've ever had a child with a high fever and they sweat profusely when it breaks, they stink. I can't imagine there was no odor in that car even if not the horrid odor of actual decomposition.