Chevrolet 2011 Volt Collision Awareness Manual page 22

Thermal Management
Systems
The Vehicle utilizes three separate
cooling systems that maintain the
proper operating temperature of the
components. The components include
the drive motor battery, drive motor /
generator power inverter module, drive
motor battery charger, and engine. The
cooling systems require a pre-mixed
50/50 solution of DEX-COOL® coolant
and de-ionized water. Tap water should
never be used in the cooling system as
it will leave deposits and cause
corrosion which effects heat sink
performance.