Your Prius should run cool, and in order to do that, you need cool fluids circulating within the engine. If the fluids are not circulating as they should, you may need to replace the water valve inverter. Here are the steps you need to take to change out yours.
• 10mm and 12mm sockets and socket wrench with extensions
• 14mm open end wrench
• 10mm box end wrench (used for the inverter coolant bleed valve)
• 24mm or 15/16 wrench (used for the drain plug to the coolant in the transaxle)
• Old pan for the coolant
- Start by draining the coolant from the engine.
- Remove both the engine under covers.
- Set the Prius ignition set to OFF.
- Remove the 24mm hex drain plug on the bottom of the transaxle. The AFT fluid drain plug is a 10mm plug. Do not confuse the two.
- Drain the fluid.
- Replace the 24mm drain plug using 29 ft. lb. torque.
- Once the fluid has been drained, you can remove and replace the water valve inverter.
- Take the black plastic cover off the radiator.
- Remove the nut and bolt that holds the water valve bracket on. The stud holds the pump onto the vehicle.
- Disconnect the connector that holds the wiring harness by squeezing the tab on the connector to remove the harness.
- Disconnect the water valve from the hose.
- Replace the water valve.
- Reconnect the hose.
- Reconnect the wiring harness.
- Reinstall the bracket.
- Replace the radiator cover.
- You are ready to add the fluids back to the car.
- Add fluid back to the vehicle with the ignition set to OFF.
- Fill it to the full level.
- Set the Prius to ON for 20 seconds or so and let the fluid level out.
- Add more fluid until it is set to full again.
- Turn the vehicle off, and use the 10mm box wrench to open the bleed valve. When you see fluid, close the valve.
- Repeat this until there is no more turbulence in the coolant reservoir and the pump quiets down. You should not be able to hear air in the system.
- Dispose of the used coolant in a responsible manner. It is toxic to plants and animals, so use caution when discarding.
If you need to replace the water valve inverter, use OEM part 16670-21010.
You will find it here.