* Coolant Temperature Sensor: This sensor, located in the engine block or cylinder head, measures the coolant temperature. Low coolant levels can cause overheating, which the sensor detects. This is *not* a direct level sensor, but the engine's computer uses it to infer potential problems, possibly triggering a warning light.
* Pressure Sensor (if equipped): Some vehicles, especially those with pressurized cooling systems, have a pressure sensor in the radiator cap or pressure relief valve. Low coolant levels would result in reduced pressure, which might trigger a warning. Again, this is indirect.
* Expansion Tank Sensor (most likely): The 1997 Lumina likely uses a sensor located *in the coolant expansion tank* (the overflow reservoir), not the radiator itself. This sensor directly measures the coolant level within the tank. Its exact location within the tank will vary, but it's typically a float-type sensor or a similar device.
To find the sensor: The best approach is to consult your owner's manual or a repair manual specific to your 1997 Chevy Lumina's engine (3.1L V6, 3.4L V6, or 3.8L V6). These manuals provide diagrams showing the location of all sensors and components. You can also look up diagrams online using your engine's specific details. Visually inspecting the overflow/expansion tank for a sensor is the most likely place to find it.
