Prius still overheating even after spending $1000 at the shop

I don't think they ever cleaned the egr and intake manifold. I am somewhat aware of the prius headgasket issue upto Gen3. I heard Gen4 also has it even though it is supposed to be fixed. I don't feel they are having HG issue right now but it could be coming soon now that they had repeated overheating issues. They said they had owned it new and never had any problems except for overheating 2-3 years ago (fixed with a new water pump) and now. For 264k miles, they've just been lucky, according to what I read in this forum and elsewhere.

 

Just to report back my latest findings:
1. while waiting for the Aisin water pump to arrive, I decided to take the air intake box off and investigate more. I found that when I ran the engine continuously to bring up the temperature until it overheated, the metal pipe that comes out of driver side of the engine got burning hot. This pipe connects to a big rubber hose that goes into the bottom right (i.e. driver side) of the radiator. I believe it's like the upper radiator hose in ICE car that flows coolant from the engine to the radiator. Also, there is a smaller hose coming off the same metal pipe. That hose routes all the way and becomes the upper hose in the recovery tank and it blew super hot coolant into the tank whenever engine overheated. Meanwhile, the big lower radiator hose on the bottom left of the radiator connects to the water pump. It was cold the whole time. Also, from the bottom center of the radiator there is smaller hose that routes to and becomes the lower hose in the recovery tank. And it was cold as well.
2. I found my old Techstream (installed in an XP virtual machine) and hooked it to the OBD2 port. I was able to use Live Test to turn on the radiator fans and water pump at will. What was perplexing though is that the test for water pump can only turn it on at 3000rpm or off but live test showed the rpm was bouncing all over the place from 0 to 1500 to over 3000 or even high, even though the software says 3000 rpm is the max. I thought, "this stll can't prove the pump is good because the rotor could disengaged or split and it is just spinning and not pushing water." I went out to check under the hood. I could hear the pump when it was on and the noise die down if I turned off the pump in Techstream. I could also feel some vibration and some gurgling noise when it was on. The vibration and noise would stop when I stopped the pump. So I am sure now the rotor is spinning. What I am not sure of is whether it's effectively push the water and why the rpm fluctuated so much?
3. when I get the new pump tomorrow I will finally have a good look at the old pump and see if it's OE and if there is anything wrong with the rotor/magnetic impeller. If it looks and spins fine, I am afraid I will have way more work than I wanted to commit to, i.e., taking off and checking the newly installed thermostate, flushing the radiator and the engine coolant passages. The one thing I really dread is engine coolant passage clogging, which I have no idea how to flush and de-clog.

BTW, Techstream found no code other than the original P0117 "engine coolant temperature sensor 1 circuit low" code, just like my Bluedriver scanner. I still think the ECT sensor is good because it shows the continous coolant temperature changes in the scanners everytime.

Here are my three shorts showing the overheating and my Techstream live test. Sorry, I still can't post the links. You can search Youtube with keywords DXW, Prius, Overheating (or Water Pump) for these three shorts:
DXW 2015 Prius overheating
DXW Prius water pump Techstream #automobile #mechanic live test1
DXW Prius water pump Techstream live test2

Test1 shows the coolant temp went up to 220F and I changed the screen to show the Target RPM and Actual RPM.
Test2 showed more of the RPM fluctuation.

Thank you all so much for your input!

 

Thank you, Parker, for posting the link. You can tell I never published any videos. In fact, I need to apologize to all of you for the horrible resolution. I used a computer to look at them and realized you can't see anything in the areas I didn't zoom in. I need to figure out how to keep a better resolution when uploading. Don't remember seeing an option though.

Regarding the ECTs, I could only find one temperature in my cheap Bluedriver's live data. And Techstream's live data screen has only one also. So that may be the one on the engine. The other one is probably buried in the EGR data section? Anyways, at least I was able to read the right temperatures from the sensor.

 

Thanks for the screenshots. That was very helpful! Could you tell me where you got the Exhaust Heat Recirculation Flow diagram? I tried to look for a cooling system flow diagram in AllData but couldn't find such diagrams other than basic component drawings and removal/installation procedures.

 

Thanks, Parker! they got the new water pump but I haven't been able to go work on it yet. There is always something else that gets in the way and drags it on and on (

 

Okay, everyone. The final diagnosis -- it is the cheap aftermarket water pump! Owner spent over $700 for the water replacement 2 years ago at another shop and got a knock-off. That was why I didn't attack that at first. But I had a strong suspicion after I flushed the heater core which was indicated in the recent garage report.

What made it harder is that the water pump never threw a code, and Techstream was able to see the pump spinning (supposedl) and control the pump in live test (stopping and starting). My own suspicion on the live test result was that the test was supposed to set the pump speed at 3000rpm max but actual speeds varied from a little over 100 to over 5000. I will test it again when I finish the repair and see if the OE pump behaves the same. Here is the video for my diagnosis:
https://youtube.com/shorts/u2VRFZ-eEwk

You can go to my channel to see other related shorts:
https://m.youtube.com/@danielwang7335

Thank you everyone for your input and moral support! I've learned a lot in this forum. Will give you the final report once I put everything back together and test the prius.

 

Good to know. However, pretty much all of the youtube videos I've seen on bad water pumps would throw a code or show no speed on the pump. In my case, Techstream could control the pump and show its speed during live test. I thought there was a speed sensor in the pump. But I took the pump out, as you can see in my youtube video, I couldn't turn the impeller rotor unless I tried very hard. So either there is no speed sensor, or the electronics in the pump was sending signals that made the ECM think it was spinning.

 

Any ways, I just put everything back together and ran the car in maintenance for nearly an hour. Fan didn't kick in until coolant temp got up to 196F (after 15-20mins). Then temp dropped down and stayed at 181F pretty much all the time. Temp never went past 197F. Heater works now. AC works. Engine runs great. Didn't notice any air bubbles. Coolant level didn't drop much. I told the owner to watch and top it off.

I am calling it a day. Thanks to everyone who contributed to this thread. I learned a lot about the Prius hybrid cooling system. It was quite an experience.

Now I need to find time to talk to this shop who lied to cover their impotence, charged my friend a bunch of money for nothing, and wasted so many of my hours! If I can't get a reasonable refund from them for my friend, I will make sure people are aware of their practice.