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Changing Inverter Coolant Fluid.

Discussion in 'Generation 1 Prius Discussion' started by elendilmir, Aug 4, 2010.

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  1. elendilmir

    elendilmir Junior Member

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    I'm coming up to 120K miles, for which the dealer lists changing the inverter coolant. I've been trying to become a bit more of a do it yourselfer. I pulled out my trusty Chilton manual, and it doesn't go into it very much. Is this something beyond operator maintenance?
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    techinfo.toyota.com will provide you with Toyota repair manual info. The process to change the inverter coolant isn't that bad, but you have to work hard to get air out of the system.

    You will need a gallon of Toyota Super Long Life Coolant (pink, which has a 50K mile change interval and is premixed with distilled water) or Toyota Long Life Coolant (red, with 30K mile change interval, and this needs to be mixed 50% with distilled water.) You will also need a replacement aluminum washer for the drain plug, as it is recommended that the washer be replaced when the drain plug is removed. These items can be purchased at the parts counter of your local Toyota dealer. Finally, you'll need a length of vinyl hose that will fit the two bleed valve nozzles located near the front of the inverter.

    The procedure is as follows:

    1) Make the car IG-ON where the instrument panel warning lights are all on (not READY). Listen to the inverter coolant pump near the driver's headlight assembly. Note that it sounds like an aquarium pump and that you do not hear air bubbles. Also look at the reservoir mounted on the side of the inverter and note there is a fluid step where the fluid at the very front of the reservoir is higher than elsewhere. Keep the sound of the pump and appearance of the reservoir in mind. You'll need to restore the car to that condition before you can declare victory.

    2) Remove the inverter/transaxle coolant drain plug located at the bottom of the transaxle, closest to the engine, and drain the coolant into a container. You need a 24 mm socket. Do not remove the drain plug which is nearby but located more towards the driver's side of the car, as that is for the transaxle ATF fluid. Measure the amount of the old coolant, then dispose of it safely; it is poisonous to pets and fauna.

    3) Replace the drain plug using a new gasket, if you bought one. Tightening torque is 29 ft.-lb.

    4) Add new coolant into the reservoir mounted next to the inverter. Make the car IG-ON, then add more coolant. You'll note that the inverter pump now sounds funny, compared to #1 above. You'll also note that there is no fluid circulating in the reservoir. Make the car IG-OFF.

    5) Purge air out of the system. Find the two bleed valves at the front of the inverter. Remove the rubber caps. Attach a couple of vinyl hoses to the bleed nipples and run up to the reservoir mounted on the inverter. Make the car IG-ON, open the bleed valves. Use an open end wrench to hold onto the bleed valve body while you use a box wrench to open the valve. Go easy as the valve is relatively delicate.

    Hopefully fluid will start to enter the hoses. Fill the reservoir as the level drops. Close the bleed valves, make the car IG-OFF. Repeat until the pump sound is restored to normal and you see circulation in the coolant reservoir with the step in the fluid level. Also, keep track of the new coolant used and compare with the amount that you drained in #1 above.

    It might help for you to take a drive around the block, while you are working to get air out of the system. Plan to spend a couple of hours on purging the air out. You cannot stop this process until the proper system operation is restored. Good luck.
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  3. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I noticed you have 2002 Prius. I did a video when I changed it for my 2006. This may help.

    [ame=http://www.youtube.com/watch?v=-yf6eCeV4M8]YouTube - 2006 Prius Inverter Coolant Change[/ame]
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  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Keep in mind that it is much easier to get air out of the 2G inverter coolant loop, than the Classic inverter coolant loop.
  5. jk450

    jk450 New Member

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    If it's convenient, the self-service owner may wish to let the car sit overnight after draining and refilling the inverter coolant. The system will often purge itself during that time. The inverter coolant can then be topped off, and the system checked for proper circulation.
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  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Thanks for the tip. Is that attributable to a heating and cooling cycle that encourages the trapped air to rise up?
  7. jk450

    jk450 New Member

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    It's quite possible. Any change that encourages the buoyancy of the trapped air bubbles to overcome their own surface tension — cooling air, coolant, or components; random vibrations — is likely to help.
  8. Solman636

    Solman636 New Member

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    Is the drain valve washer/gasket same as the one for the oil pan? I just bought an 8 pack. :) Also, Mr. Wong's youtube is very helpful and really simplifies the process for the 2G like mine...or at least I hope so. Will do the job tomorrow and let follow up. Thanks.
  9. Mendel Leisk

    Mendel Leisk Senior Member

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    Likely the washer is different. Check with your dealership parts dept.
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The inverter/transaxle drain plug gasket is aluminum and a larger diameter vs. the engine oil drain pan gasket which is made of composite material and smaller. So you definitely need to buy an aluminum gasket from your Toyota dealer, and if you also plan to replace the transaxle ATF then buy three. Use a 24 mm (or 15/16") socket to remove the drain plug. Tightening torque is 29 ft.-lb.

    It is pretty easy to change the 2G inverter/transaxle coolant and get air out of the loop. Listen to the sound of the inverter coolant pump when the Prius is READY, before you start the work. Your job is to restore that quiet sound as you are adding fresh coolant and purging the air out - if you hear bubbling then you know that air remains in the system.

    The YouTube is courtesy of usbseawolf, not me BTW.
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