Improvement in mpg after changing inverter coolant?

I would not expect any changes. Either the cooling system keeps inverter temperature "low enough" (normal operation) or it doesn't (& sets codes - shuts down).

Posted via the PriusChat mobile app.

 

I guess if it was overheating really badly and constantly throttling back and not allow you to get enough electric motor because of not enough battery I guess your gas mileage could come down a little and of course that would be rectified once the inverters cool can stay on as long as it needs to to run the battery up as high as it needs to go so it can power the engine properly.

 

Same volume before and after? Then no change at all in cooling properties would be expected. Coolant is usually changed to keep the pH high enough that it doesn't start chewing up the metal it passes over/through, not because it isn't cooling well. Coolants have chemicals in them to keep the pH basic, but these break down and/or get used up over time and the coolant becomes acidic. Hence the "change your coolant" periods the manufacturers set in their maintenance instructions.