Inverter coolant at 150K?

I would follow the maintenance schedule that came with the car.
That being said, I haven’t changed any of the fluids in my ten year old 80,000 mile gen 3

 

Canadian schedule told me to change both* coolant circuits at 10 years or 160k kms, whichever comes first. Honoured that a couple of years back, at 10 years, around 85k kms.

Maybe overkill, who knows. DIY’ing, only cost about $50 for two bottles of the Toyota coolant.

* Even verified with Toyota Canada. What they say is at odds with this decal:

^ Try Amayama, better price, less BS. Consolidating purchases avoids multiple shipping charges, and try to keep it from just one country (it’s either Japan or UAE).

 

Editorial comment on the above pic: I believe it’s a Canada-only bilingual label, English text states miles, and French is kilometres lol.

 

The additives (to prevent corrosion) degrade over time and with temperatures (of the system). Failure to change out the coolant could result in failure of the inverter assembly due to corrosion, which is terribly expensive. I wouldn’t risk it.

 

Inverter coolant change looks sim to 3rd gen, and is relatively easy. I'd guesstimate dealership charge should be around $150, it's easier than engine coolant change. For curiousity, or if you're open to DIY, see attached:

 

I believe the inverter coolant system also cools the transaxle so it would be doubly more important to change it.

 

Yeah drain bolt is in underside of transaxle. IIRC it's socket-head cap-screw style, takes a 10 mm hex driver IIRC.

 

Changing inverter is as easy as changing oil. Do the job yourself. Follow Mendel’s link for instructions. I just did both of these in less than 30 min at 100k. Coolant out of both was super clean, I know I could have gone way longer. But your vehicle’s coolant may be/look/breakdown differently.