Do you think the gas tank is IN the engine bay or something? The hottest thing underneath a gas tank might be the exhaust… The ignition temp of gas is something like 500F/260C… Without spark… it’s not going to happen just out of the blue. An Exhaust CAN get that hot… But under most normal uses, basically all normal cars won’t get that hot (racecars and other “performance cars” probably will get hotter than the ignition temp of Gasoline).