I am not directly familiar with the types of automotive temperature sensors, so I looked it up. To my surprise, the most common sensors used for engine coolant temperature and engine oil temperature are thermistors, which are resistors that change with temperature. They are cheap, have a high sensitivity, and can be made to a precise value so that they can be replaced without calibration. The most common ones also have a negative temperature coefficient, i.e., the resistance decreases with temperature. The high sensitivity allows them to be directly connected to a dashboard meter (needle-type) without additional electronics. The meter could also provide a pickoff to be sent to the central computer in current designs, but then an amplifier and ADC would need to be added.
We have developed some circuits for in-car temperature measurements with thermocouples, and we show one using a Type T thermocouple, which has good range and sensitivity. This is in our Circuit Note CN0281.
