==Origin== In the early years, automobiles had their radiator caps outside of the hood and on top of the grille which also served as an indicator of the temperature of the engine`s coolant fluid. The Boyce MotoMeter Company was issued a patent in 1912 for a radiator cap that incorporated a thermometer that was visible to the driver with a sensor .... Found on http://en.wikipedia.org/wiki/Hood_ornament