Balancing Act

DIY: How to Exchange the Inverter Coolant On Your 3rd Gen Prius

Before you proceed with this maintenance procedure, make sure you have access to a flat and level surface area. You will also need two jack stands to support the front end of your car so you can gain access to the inverter coolant drain plug.

Toyota recommends inspecting and topping off the inverter coolant reservoir every 5,000 miles and a complete drain and replace every 100,000 miles. So I’m 20,000 miles late to the game.

My local Toyota service center charges $159.95 for this procedure. If you do it yourself, material cost is between $26.00 ~ $52.00 for two 1 gallon jugs of Toyota’s Super Long Life Coolant (SLLC), depending on where you acquire them.

I only used up 3/4 of one gallon jug for this inverter specific service, but it’s good to have extras (2) on hand if you intend to also exchange the engine coolant and to top off every 5,000 miles.

In addition, you’ll need a hydraulic floor jack, 2 jack stands, drain plug gasket, ratchet with a 10 mm hex bit and a drain pan. A creeper will also make the job easier and keep your back clean.

The entire inverter coolant fluid exchange service takes about 45 minutes of your time.

Tools and Materials Needed

Toyota’s Super Long Life Coolant lasts an incredibly long time and comes pre-diluted, meaning it is ready to use right out of the jug. You do not need to pre-mix it with water as you would with the traditional green stuff from the local auto supply store. You will need at least one gallon, but having two jugs on hand just in case is never a bad idea. Regardless, it’s a good idea to have an extra jug laying around in the event you need to top off the coolant reservoir.

Removing the Engine Under Cover

Because you’ll be working underneath your car, safety goggles are an absolute necessity. Do not attempt unless you are wearing a pair.

Working on a flat and level surface, place wheel chocks on the rear wheels and then jack up the front of the car. Place a jack stand on each front jack support on the chassis.

In order to access the inverter coolant drain plug, you’ll need to remove the engine under cover. This involves removing six 10 mm bolts and 13 push-pin retainer clips. If the clips are worn and brittle, this would be a good time to replace them.

Removing both clips and bolts should take you approximately 15 minutes if it is your first time and subsequently quicker. This is what the cover looks like and where the bolts (yellow) and clips (red) are located to visually help you expedite the removal process:

Since removing the engine under cover is an involved procedure in itself, you might want to consider performing these maintenance service at the same time if possible:

Doing all aforementioned services together should take you approximately 3 hours.

Exchanging the Inverter Coolant

Believe it or not, the hardest part of this maintenance procedure is done. The following steps should take you approximately 20 minutes.

Step 1

Remove the cap on the inverter coolant reservoir and set aside. Locate the inverter coolant drainage plug. This is a 10 mm hexagonal bolt perpendicular to the axle and close to and beneath the transmission fluid filler and drainage plugs. Do NOT mistaken it for the automatic transmission fluid drain plug, which uses the same 10 mm hexagonal bolt.

I used a 18″ breaker bar to break the bolt loose, then hand untighten the bolt:

Place a drain pan beneath the plug and carefully and slowly undo the 10 mm hexagonal bolt – be sure to wear safety goggles as the draining coolant WILL splash.

Allow coolant to completely drain, about 5 minutes.

Step 2

Discard the old gasket and replace with a new gasket.

Replace and tighten the 10 mm hexagonal bolt with new washer and replace the engine under cover. Torque spec: 39 N·m (398 kgf·cm, 29 ft·lbf)

Step 3

Using a funnel, slowly pour the Toyota Super Long Life Coolant into the inverter coolant reservoir:

The inverter coolant reservoir will slowly drain, so you will need to fill and wait repeatedly up to 2-3 times.

Always fill to the FULL mark.

Step 4

Once the inverter coolant reservoir stops draining, get your Prius into READY mode (hold down the brake and press START). Wait 5 seconds and turn off the Prius before the internal combustion engine (ICE) kicks in. The inverter coolant should be cycling through the inverter coolant system, draining the inverter coolant reservoir once again as the coolant travels through and fills up the inverter coolant system.

Fill the inverter coolant reservoir with coolant up to the FULL mark and repeat the above step.

Repeat up to 5 times until the inverter coolant reservoir stays at the FULL mark and doesn’t drop any further:

Replace the inverter coolant reservoir cap and tighten. Take your Prius for a short drive to fully cycle the coolant, then examine the inverter coolant reservoir again to check fluid level. It should remain at FULL. If it dropped, top off until full. Check for leaks.

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