A GM article explaining the Chevrolet Volt’s cooling/heating systems notes that the power electronics coolant loop is designed to insure the main underhood electronics do not overheat during use. It is essential that the heat developed by the power inverter module and the plug-in battery charger while operating the Volt or when plugged in be dissipated in order to prevent damage to the components. The Chevrolet Volt uses a high flow 12-volt electric pump to create and control the coolant flow which passes through — in order — the plug-in battery charger assembly, the radiator, the power inverter module (PIM), and then back to the pump. The power electronics cooling system radiator is the upper half section of a dual radiator assembly that is common with the high voltage battery cooling system.
The power electronics cooling system also uses an air separator device to prevent air-bubbles from affecting cooling performance and utilizes a surge tank that acts as a coolant reservoir, and facilitates the routine addition of coolant via a pressure cap.