Abstract: A cooling system includes a coolant tank, a coolant sensor assembly, and a controller. The coolant sensor assembly includes a sensor package having a first end and a second end, the sensor package including a partially transparent or semi-transparent sight glass housing a coolant level sensor and configured to receive a flow of coolant therethrough. The coolant sensor assembly also includes a first valve coupled between the first end of the sensor package and a coolant tank, a second valve coupled between the second end of the sensor package and the coolant tank, and a third valve coupled in flow communication with the second end of the sensor package. The controller is configured to execute one more diagnostic self-tests for the coolant sensor assembly and the cooling system.