Need help! Gas engine overheating. Cannot resolve.

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Sergey K, Apr 1, 2019.

  1. The Critic

    The Critic Resident Critic

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    I have never had any issues with bleeding this cooling system so I am skeptical that air pockets are the problem here.

    I assume that you are not losing any coolant when the system is not overheating.

    I still think your issue is related to water flow, or inadequate flow.

    Two questions that I have are:

    1) Was the water pump you installed, a Genuine Toyota or an Aisin? If not, start there.
    2) When the car is overheating, pull over and physically feel the radiator hoses and the heater core hoses. All 4 should be hot. If not, I think you can proceed with troubleshooting there.

    My guess is that you either have a defective water pump or a clogged heater core, one (or both) of which are causing flow to be inadequate during high load conditions.
     
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  2. mjoo

    mjoo Senior Member

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    Without a loss in MPG or knock, I think the control valve on the exhaust heat recouperator is a possible failure mode.

    Pixel XL ?
     
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  3. The Critic

    The Critic Resident Critic

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    That crossed my mind too. But I would expect the heat from that unit to cause the engine to overheat all of the time, not just under heavy load conditions. But it is certainly a possibility too. Perhaps the OP can eliminate flow to that circuit temporarily for testing?
     
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  4. Sergey K

    Sergey K Junior Member

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    How would I do this?
     
  5. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Are we sure that the new water pump is.....pumping?
    Who replaced it?
    Is this unit connectorized?
     
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  6. Sergey K

    Sergey K Junior Member

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    I replaced it myself. It is a brand new AISIN water pump. I connected and tested it before installing it to make sure it was working. It spun up very well. I can also feel and hear the vibration from the pump when it's running.

    My guess also is if the water pump wouldnt be working, the car would overheat at lot sooner and at idle as well.

    And if the pump is faulty, you usually get an engine code as well.
     
  7. Sergey K

    Sergey K Junior Member

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    So I tried Mendel's advice. I ended up removing the coolant temp sensor itself instead of the smaller upper hoses (the clamps on the hoses were extremely hard to reach and I was able to remove the temp sensor without removing any other parts). A little bit of coolant leaked out. I spent about 1/2 hr squeezing all the coolant hoses with the coolant reservoir cap off and coolant temp sensor removed (highest point in cooling system).

    I added a tad more coolant. Not sure if actual air escaped or just some coolant leaked out when I removed the sensor and squeezed the hoses.

    Drove the car up a few hills around my house at high speeds and I couldnt get the temp to go over 194F. It is very hard to recreate this issue unless you live by some mountains, which I dont.

    When the coolant was at 194F, I pulled over and felt all the hoses coming from the radiator. The incoming thick hose from the engine (driver side) was really hot. The outgoing thick hose on passenger side was slightly warm (but much cooler, maybe slightly over ambient outside temp which was 60F) than the incoming hose. The other 2 smaller hoses were warm as well. It seems like the radiator is doing its job?

    I will take the car to work tomorrow (1hr drive over many hills across 5 different highways). Thats usually where it kept overheating in the past.

    I couldn't check the fan speeds because its almost impossible to hook up 12V to them when they are installed in place. I'd have to remove the fans which I didnt have time for today.

    Any other ideas would still be appreciated.

    Ill keep you posted with my drive tomorrow.
     
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  8. Mendel Leisk

    Mendel Leisk Sand Pounder

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    good sleuthing (y)
     
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  9. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    The reason I asked whether or not it was connectorized had to do with direction of spin (always look where you've been) but...yeah....it was probably air bound.
    Keep us posted.....
     
  10. Joele3

    Joele3 Active Member

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    Sounds like the issue I have. I tried bypassing both heater core and exhaust recovery tank. All the coolant hoses coming from firewall and down below towards exhaust. I had them all routed to each other. Just EGR cooler and gas engine I left in the loop. Same result got hot once I revved up driving. I had the reservoir out and hanging from the hood to bleed the air out. Once I felt both radiator hoses warm up I went drove it fast thinking the coolant finally was circulating good enough. Same result got hot once I punched it. Now my passenger side hose doesn't get hot at all.

    My next test will be drilling out thermostat so theres no restriction there. I have three thermostats laying around. One is Gates branded and two OEM. I just took a break from working on my car didn't wanna blow it up from frustration.
     
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  11. ASRDogman

    ASRDogman Senior Member

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    Have you changed the thermostat? Sounds like it's stuck shut.
    Maybe that's why the water pump went out.
     
  12. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Holy carp!
    I don't remember that being checked/changed....
     
  13. ASRDogman

    ASRDogman Senior Member

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    When you replace it, if there's a little check ball at the top, remove it so it's just a hole.
    If no hole, drill a small one at the top. This helps in the bleeding.
     
  14. Grit

    Grit Senior Member

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    Have you pressure test the radiator system to see if it holds proper pressure? It’s a pressurized system.

     
  15. Sergey K

    Sergey K Junior Member

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    Gents, thank you all for all your help.

    I drove to work and back (2hr drive all highway) and in the spots where my coolant temp used to spike to 235F, it now will not go over 192F no matter how hard I try. It stays steady at 190F the whole way and as soon as it rises to 192F, theres a sudden temp drop right back down to 187F. I also took it to a very, very steep hill after all the highway driving and floored the gas pedal and got the same positive result, never over 192F and immediate drop back to 187F, then stabilize again at 190F.

    Im fairly confident the issue is fixed.

    Big shout out to Mendel Leisk about giving me the idea of removing the small upper hoses which led me to remove the coolant temp sensor.

    So to summarize, I had a faulty water pump (but spent tons of time and money chasing other parts) and then I had some air bubbles in my cooling system that prevented the coolant from circulating properly.

    The key take away is if when you're refilling coolant, remove the coolant temperature sensor (highest point in the cooling system) and remove the radiator cap before bleeding the system. This opens up escape ways for air to leave the system from both sides of the engine at the same time.

    I also liked Joele3's idea to unscrew the coolant reservoir and prop it up higher as well.

    Thanks to all who contributed. I hope I never see the engine overtemp light on my dash ever again!
     
    #35 Sergey K, Apr 4, 2019
    Last edited: Apr 4, 2019
  16. Mendel Leisk

    Mendel Leisk Sand Pounder

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    The coolant temp sensor is up at the top there, in that plastic connector that used to also have the bleed screw?

    Maybe then, the sensor was sitting in an air pocket, giving false (low) readings?

    Frustrating that they deleted the bleed screw.
     
  17. Sergey K

    Sergey K Junior Member

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    Yes. My Prius still has that weird 4 way plastic connector up there. 2 of the ports are used for water flow through it into the passenger cabin, 3rd port the coolant temperature sensor screws into, and the 4th port that sticks up is nothing but a sealed plastic pipe thats useless.

    I took that 4 way contraption out before because I thought I lost the white bleed screw cap (the screw cap is missing on mine but I saw it online in pics on other models).Turns out it is a plastic pipe thats sealed at the bottom. Nothing there. No hole, no valve, nothing.

    Bizarre design by Toyota.
     
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  18. Sergey K

    Sergey K Junior Member

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  19. mjoo

    mjoo Senior Member

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    More planned obsolescence by Toyota? I wonder how many head gasket failures this causes?

    Excellent write-up Sergey

    Pixel XL ?
     
  20. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I was thinking maybe you can order a 2010/2011 style "air release valve", but having no luck finding it on McGeorge Toyota parts.

    IMG_0294.JPG
     
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