on the service manual it says -
COOLANT LEVEL IN RESERVE TANK (for Inverter)
(a) The coolant should be between the LOW and FULL
lines when the coolant for inverter is cold.
If the coolant level is low, check for leakage and add
TOYOTA Super Long Life Coolant (SLLC) or similar
high quality ethylene glycol based non-silicate, non-
amine, non-nitrite, and non-borate coolant with long-
life hybrid organic acid technology up to the FULL
if you want to drain it.. here's the plug (somehow it's not a DIY thing because it needs to be bleed properly);
DRAIN COOLANT (for Inverter)
Collect the drained coolant and measure its volume
to establish a benchmark. When adding coolant,
make sure to add more coolant than the measured
(a) Remove the inverter reserve tank cap.
(b) Using a hexagon wrench (10 mm), remove the drain
plug indicated in the illustration and drain the
(c) Using a hexagon wrench (10 mm), install the drain
plug with a new gasket.
Torque: 39 N*m (398 kgf*cm, 29 ft.*lbf)
ADD COOLANT (for Inverter)
Coolant (for Inverter) capacity: 2.9 liters ( 3.1 US qts, 2.6
(a) Add coolant from the reserve tank.
(b) Connect the intelligent tester to the DLC3.
(c) Follow the intelligent tester screen to perform the
active test of the water pump.
(d) While adding coolant so that the coolant level is
kept between the FULL and LOW lines.
If the water pump operates without a sufficient
amount of coolant for approximately 5 seconds, the
protective circuit will activate to stop the water pump
for approximately 15 seconds. If a sufficient amount
of coolant is added, the water pump will start
When the operational sound volume of the
water pump becomes small or when no air
bubbles can be seen in the inverter reserve
tank sub-assembly, bleeding of the coolant
system is complete.
(e) After bleeding is completed, stop the water pump,
add coolant to the FULL level, and install the
inverter radiator cap.
Make sure to add more coolant than was drained