The 1998 Chevy Lumina LTZ 3.8L doesn't have a dedicated radiator coolant level sensor in the traditional sense like some modern cars. The cooling system relies on the engine coolant temperature sensor (ECT) and potentially a low coolant level warning light in the instrument cluster which is triggered by other means, such as a low pressure sensor in the cooling system or, less likely, a simple float switch somewhere in the system. There's no single sensor directly measuring coolant level *in the radiator* itself.
To check the coolant level, you need to open the radiator cap (carefully, when cool!) and visually inspect the coolant level in the radiator. The coolant should be near the "full" line or between the minimum and maximum markings. Keep in mind that the coolant level will appear lower when the engine is cold.
