the bedford ca was designed in an era when semi-conductor devices were state-of-the-art, and not affordable for automotive applications. water temperature was thus measured mechanically, via a capillary tube connected to capsule containing a volatile liquid. the capsule was screwed into the body of the water pump. as the engine coolant temperature increases, the volatile liquid expands, altering the pressure on a mechanical linkage in the water temperature gauge, which moves the position of the needle. later models used an electric gauge.