Random Overheating

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by casi000, Oct 1, 2019.

  1. Robert Holt

    Robert Holt Senior Member

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    Ok, good luck with this!
    As you had it in maintenance mode and could observe the process, did the radiator fan come on as it should when the ECU detects the engine temp getting to the upper limit? Because if the fan was operating as it should and not playing a role in these overheating events, then the sticking thermostat is looking more likely. ( I used to take the thermostat and test it by putting it in a pan of water with a thermometer and then visually checking that it opened at the correct water temp, but that was the Good Old Days when cars and airplanes were simple! ) I absolutely agree with going OEM on the new thermostat.
     
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  2. casi000

    casi000 New Member

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    No dice so far on the thermostat. Replaced it and flushed the coolant (that should rule out air in the system too). I still need to take it for a drive to verify (making sure my revving while parked in maint mode didn't cause the overheating). The good news I guess is it seems easy to replicate the problem. Fluid looked clean when I flushed it. The symptoms are strangely consistent: cold engine (usually), warms up normally, does not level off at 190, keeps going to around 225, boil over, levels back down to 190 in under a minute, stays 190-200 rest of the trip. Is there an easy way to verify the water pump is working without a techstream? I am not getting any codes but I found another post that had WP issues with no codes.
     
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  3. Robert Holt

    Robert Holt Senior Member

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    Nuts! This is way weird, because I would think that if the water pump had failed, your Prius would continue to overheat and boil over on a repetitive basis as you were driving.
    You did check that this fan at the rear of the radiator was properly activated as the ICE got to the 198-200 degrees Fahrenheit range, right? I ask because if the fan did not activate correctly (e.g., faulty triggering circuitry or burned out fan motor) , the car would overheat while standing still, but might still run successfully at highway speeds do to the velocity-induced airflow through the radiator.
    448010E0-97B3-4896-90B5-A8975A982F48.jpeg
     
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  4. Joele3

    Joele3 Active Member

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    I had this same issue. Try bypassing the heat exchange. If your water pump is making funny noises at the higher temps it may already be toast. I don't recommend replacing the water pump without first bypassing the heat exchange. You'd just burn up another water pump, I know i've burned up quite a few of them. I bypassed everything but left the old water pump in the mix. Temps still increased at idle in maintenance mode. I'd rev it and stop at around 105c. I put a new water pump w/ heat exchange out of the loop. No heating issues. Raise the reservoir to speed up bleeding the air. Theres some sort of door that will close the flow of coolant from entering the heat exchange but I don't know where and if its accessible. Good luck.
     
  5. casi000

    casi000 New Member

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    Hmm. Heat exchange? I will give it a shot. Is this in with the EGR stuff?

    Edit.. this one? https://priuschat.com/attachments/ehrs-2-of-2-png.66689/
     
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  6. Joele3

    Joele3 Active Member

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    Yes thats it. I replaced the actuator where it controls the door for back pressure of the exhaust. But it didn't resolve problem and last time I looked under it was stuck open.
     
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  7. casi000

    casi000 New Member

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    Actually the theromstat may have resolved it, I took it on a couple of trips and no issues so far. I *think* the pushing it to 2k rpm while stationary in maint mode caused overheating. But I will give it another week or so before I call it. Anyone know if the Prius is a 185 or 190 stat? Based on torque it seems to be 185, just wanted to verify.
     
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  8. casi000

    casi000 New Member

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    5-6 trips and no issues since, it looks like the thermostat did the trick. Hey every now and then it's not the worst case scenario, even if your 2ZR is an oil burner! Thanks for the help!
     
  9. Robert Holt

    Robert Holt Senior Member

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    Yay! On the new thermostat or its packaging, was a specific temperature to open listed? I have a hazy, 40-year old memory of the opening or fully-open temperature being stamped in the metal ring surrounding the actuating plunger thing, but heaven only knows what they do nowadays!
     
  10. Mendel Leisk

    Mendel Leisk Senior Member

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    Disclaimer: missed that this is Prius c, my response was for 3rd gen Prius. Might still apply though. And yeah, don't have Prius c Repair Manual:

    Thermostat might be rated 180F: "176F to 183F" is mentioned in a test procedure, in the attached, as the point at which the thermostat starts to open.

    upload_2019-10-19_13-46-39.png

    And this site indicates that the temp rating of a thermostat is the temp it commences opening at:

    upload_2019-10-19_13-41-49.png

    Stant
     

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    #30 Mendel Leisk, Oct 19, 2019
    Last edited: Oct 19, 2019
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