Thorium-Fueled Automobile Engine Needs Refueling Once a Century.
I can imagine a billion people buying these cars and then humanity falling into a dark age in which fuel and an understanding of internal combustion and basic mechanics is lost. The cars are considered spirits from above and worshipped as gods. Rituals are performed around the vehicles to prevent issues such as flat tires and other routine wear and tear.
At the turn of the century all of the cars suddenly stop working, and humanity considers this the end of the world. The gods have left the planet and have forsaken them.