Very [loud] whining vacuum sound, super fast overheat, what happened?

I have been dealing with some overheating issues on my 2012 Prius recently and was told that it might be the thermostat because at the same time while overheating the passenger side heat went out and then all the heat went out.

The other night while driving at 40mph I noticed that my overheat light came flashing on. and then as I got closer to home in that 5 minute span it was overheating at 20mph. And then it became 5mph.

It went as followed:
1. Car overheating all of the sudden
2. Car overheating excessively with solid overheat light even at declining speed.
3. Weird sputter of a vacuum.
4. Vacuum sound gets very very loud and doesn't go away.
5. Now upon starting vacuum sound is running.

The whining sound I have never heard. I thought the coolant maybe went low and so it was sucking like a vacuum for coolant. Well, I got out of the car to check the coolant and it almost bursted out as usual. The top hose for the coolant area was super cold and its not usually like that either when its been running for a while.

I attached a few videos to hear whats going on. It's so loud I cannot pinpoint exactly what it is. It's coming more from the left side of the engine bay where the water pump is.

First video shows the car starting and the sound appearing. Second video I did a sound walkthrough with my phone to see if it picked up more sound from a given area.

vid 1
https://youtube.com/shorts/UWZ32Gs0R-M?feature=share

vid 2
https://youtube.com/shorts/bCv2DWcqZaE?feature=share


If I can find anything I will update this post so others can learn from it as well.

Update 1:
I replaced the thermostat before creating this thread. That was the theory of what was going on but did not fix the noise. Maybe it fixed the heat but that loud sound is the goal to fix here. And in fact the thermostat was stuck closed.

 

that’s what I have been trying to make sure is going on.

I don’t have a lot of cash on hand so I wanted to make sure that this was the issue before I start buying more parts that don’t fix the issue.

Thank you for the input.

 

Update: Bought a used water pump from another Prius being parted out.

I think that is water pump is bad as well. I hear some rattling with it while the car engine is idle and the engine is not running (only electric).

So the whiny pitch was still intermittent while driving. I figure if this is a bad water pump it probably isn't going to fix the issue either.

I have my car running in maintenance mode with it on a hill to see if their is air bubbles in the coolant.

Well as I sit here I hear some loud swish/knock and then suddenly the heat comes back on for just a little bit, and then it goes back to cold.

The sound is coming from the firewall area from what it sounds like. So maybe the heater core is clogged?? While I am typing I just heard another burst and then the heat came back on for a sec with a lot of heat and then back to lukewarm temp.

 

Update:

The car seems to go back to cold air after sometime. If I have the coolant cap taken off and the car running in maintenance mode the heater will blow very cold air and the. I hear a POP/FLUSH sound coming from the firewall nearby the feet area where the heater core tubes are at.

If the coolant cap is on, the coolant flush sound will not happen. It only happens when the coolant cap is off.

 

I had used Bars and Leaks before.

 

Since 80k miles I’ve owned it. Right at 150k the car started experiencing symptoms of bad head gasket so I did use a sealer a few months ago.

That’s the theory of a heater core needing to be flushed.

 

Update:

Flushed heater core and nothing unusual came flowing through it. Flowed perfectly so I guess that’s not the issue either.

 

Update:

For some reason there is something about taking the radiator cap off, and then pressing the acceleration so the car hums a bit.... well after 10 minutes of doing that all the heat comes back fully. I was able to get the car back on the road up to 60mph and then BOOM overheating and all the heat just disappears again.

 

- replaced thermostat
- Flushed heater core
- Replaced water pump


When I take the radiator cap off and let the car run with the heat on in maintenance mode the heat will return after about 10 minutes because it gets ice cold and then I hear some fast sloshing sound really fast like a pipe burst and then it restores. But after a minute or so it returns back to being cold and repeats the same process.

 

Update:

installed brand new water pump and it didn’t change anything.

at car idle this sound is going on:

https://youtube.com/shorts/ETVTs6CuBsI?feature=share