Help! Prius overheating light and losing coolant!!

Check that the bleeder cap is fully tighten. I changed coolant the other day, while refilling, coolant constantly leaked out. The bleeder cap wasn’t all the way in and coolant exited that direction

 

How many miles or km on your Prius?

I would guess that your water pump is going bad. I recommend that you replace it with an OEM pump.

Once you fix your overheating problem, please come back and report what you did to fix the problem.

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With the proper software you can see and feel what your water pump is doing and if it's not you can read what it's supposed to be doing like you can see the RPM of your water pump with the proper software connected to the car If you look here on various posts you'll see what goes on with the water pump at reasonable mileage The plastic starts to come off the impeller piece that floats in the body of the pump It kind of works like a washing machine pump out pump a modern one the impeller is not connected to the shaft of an electric motor the impeller is the rotating part of that assembly and some mag drive type of pump if you will they get eaten up internally when you take your old one off and you take the silver cover off the back side of it and withdraw the impeller you'll see all the plastic cracking and peeling and it can't even rotate in the hole it sits in when you get a new pump you won't have to take it apart you'll be able to spin that impeller with your hand or your finger or a screwdriver which you can't do on the pump you're taking out right now or if you can you can barely move it because it's all stuck and screwed up internally and you'll see that when you undo it obviously the new one won't be like that The cheap replacements the impeller is wrapped and very cheap plastic that starts to fall apart within a month of it being installed on your engine I verified this and did this twice Good luck.

 

Sounds like a failed head gasket

 

You're really going to want to get a good mechanic to run diagnostics on it....could be horrible news or something minor and fixable. This could be one of those times you go to the dealership to get them to use their very expensive TechStream to diagnose. Keep us posted!

 

If the water pump has not previously been replaced, I am 95% sure that it is going bad and needs to be replaced to fix your overheating problem. It would also be a good time to replace the thermostat and use new coolant when you fill it.

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It does not sound like a failed head gasket to me, but overheating of the engine can lead to a head gasket failure.

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Without the cap, air pressure will rush out including coolant thus no pressure for coolant to push through. When I filled coolant back to the b line, some of it spilled out of the bleed cap. It’s a black cap shaped like a tire stem cap but rubber material.

 

Could somebody photograph whatever it is you guys are calling the "bleeder cap"?

 

Ah. It's not the case that you need the rubber cap there to have operating pressure in the cooling system. That nipple goes through to the filler neck above the seal of the pressure cap. So when you have your pressure cap installed, nothing is going to come out of that nipple unless the system pressure goes above the limit (108 kPa?) marked on the pressure cap.

So that only happens if the system overheats. It looks like you've had some coolant come out there, but then you knew your car was overheating, so that's why it came out.

If anything is coming out there at less than 108 kPa system pressure, the pressure cap is bad.

If you have the pressure cap out and you're pouring coolant in, it's not impossible to get some out of that nipple, as without the pressure cap in place, it's just open to the filler neck you're pouring the coolant into.

The rubber bit that comes on that nipple just kind of deflects the stream of escaping coolant if the pressure cap vents. You can see the way the nipple's designed, the rubber cap won't seal it off, but will direct the coolant sort of underneath. Without the rubber bit, any overpressure vented coolant just jets straight out.

 

That is correct. You do not need the rubber cap.

Are you still driving your car? If I were you, I would not drive it until the water pump is replaced.

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I've never seen a rubber "bleeder cap" (which seems an inappropriate name for a hose or nipple) there. It must've gone AWOL before I bought my Prius used.

If poured into the coolant bottle carelessly, coolant does tend to escape out that plastic nipple.