I could be wrong but I'm under the impression the inverter coolant is the same as the coolant used in the radiator. In fact it might be part of the same system like on my 2004 Prius. As far as DIY, I don't think any manual tends to say that for some obvious reasons including keeping their dealers in business doing all that for you. I'm sure a smarter user will correct me if I'm wrong on all this.😊