Have a 2012 Prius that started losing reservoir coolant about 6 months ago, no leaks just disappearing , coolant dash light came on a couple of times.. took to mechanic replaced reservoir cap and refilled.. was good for about another 6 months then reservoir was very low again and refilled..about 1 week later tank was very low again so went to mechanic and he thought may be leak in tank as he saw some signs of leaking so replaced tank… wife took on 300 mile trip and check fluid and it was still full.. drove back a few days later another 300 miles and reservoir was very low again . Any ideas what could be causing this? Dreaded head gasket ? Any help would be greatly appreciated!
How many miles on the car? It is not a bad head gasket yet, but overheating the engine will lead to a bad head gasket in the future. The problem is the electric engine water pump is going bad! Do NOT drive your car at highway speed or up hills that require a lot of throttle until you get the pump replaced! I recommend you only use an OEM pump purchased from a Toyota dealership. Do a search on this Gen 3 forum, and you will find many threads with the same symptoms. I am baffled why the mechanic did not replace the engine water pump since you have the P148F code.
P148F is the engine water pump overrevolution (spinning too fast). That can happen because the plastic impeller on the pump breaks, so now the pump only spins without pushing any coolant. That's a problem you fix by replacing the pump (or some people fix by replacing just the impeller, which Toyota doesn't sell separately, but some sources do). It can also happen if the coolant gets so low that the pump is spinning in air instead of pushing coolant. That's a different problem, needing to be fixed by finding out where the coolant is going and fixing that.
