HELP! Prius overheating

How much coolant did you put in? It normally would take about 1.5 gallons or more.

You should wait until the car is nice and cool, then open the radiator cap and fill it again. There are probably air bubbles in there and not enough coolant.

 

The car has multiple water pumps and two separate cooling loops, one for the ICE and one for the inverter and MG1/MG2. Is the OP referring to the mechanical one mounted on the ICE motor, the inverter pump, the thermos pump, or the heater pump? Probably the ICE loop since I don't think the inverter loop could handle temperatures that high.

If the OP digs around on this forum there are diagrams of the cooling loops to be found. I also strongly suggest watching "eyeonaiman"'s two youtube videos about changing the Prius ICE coolant.

The OP should assume that some previous owner messed up the car, couldn't fix it, and then sold it. The hose routing could be wrong. Or maybe they put stop leak in it and both the heater core and radiator are now jammed with that crap. It would explain the symptoms...