Even if the car catches fire there is little chance the ammo will "go off" in the conventional sense of the term. I have seen numerous rounds that sustained fire damage. Everyone had the bullets intact and the primer missing. When the temperature gets high enough to "cook off' the powder/primer, the pressures are not contained like they are in the chamber of a firearm. The lightest component, the primer, is the first to pop out. It does not go far and there is a flare off through the flash hole in the case. The bullet (the projectile) has far more mass (weight) and thus, far more inertia than the primer so it tends to stay put. Simple physics actually.
For clarification, the term "clip' is commonly misused. A clip generally is used to load a magazine. A clip generally holds the base of a cartridge. A clip generally does not have a spring. A magazine generally completely encloses a cartridge, has a spring under the cartridge to facilitate feeding.
A clip and a magazine are two totally different things.
I know, I know. I am probably being too literal. I choose to be specific about things to avoid confusion. The internal combustion device under the hood of the your automobile or truck is not a "motor", it is an engine. Thingie and whachamacallit are not normal parts of my vocabulary.