What is this fluid on 2003 toyota prius?

Does youe under hood even look like this, and what does it say on the cap? Click image

Yes that is what it looks like

It says DENSO on cap, and don't open when hot

I thought I could find something on a Prius Forum. No luck..sorry

Ok, it's just seems weird for it to be an overflow tank since it had a FULL line and LOW line marked on the side... The engine coolant container is over on the left hand side under hood.

That's why I took if off, had second thoughts. But does it say anything else on cap. Like ":use only XXX fluid "?

No that's all it says on cap

Thanks for trying!!

Its called INVERTER COOLANT FLUID!! Must be changed every 120K miles. It has to do with your car's A/C and heating and is related to the water pump.

Thanks!