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No heat on idling, occasional overheat light on/off

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by DannyK, Feb 5, 2023.

  1. DannyK

    DannyK New Member

    Joined:
    Mar 13, 2022
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    Location:
    Virginia
    Vehicle:
    2010 Prius
    Model:
    Three
    I started having some heating issues on 2010 Prius. Occasionally when the car is completely warmed up (20+ mins driving) on idle (long stop sign, parked with car running) vents start blowing colder and colder air until it's just cold. When I start driving - all goes to normal. Also there were two times (today was second) when coolant overheat light pops up. I park, turn off the car, wait couple of minutes - it goes away for good, driving after that for 30+ mins, doesn't come back. Engine(!) coolant level is on full and doesn't leak (don't even remember when the last time I refilled it). Water pump on Prius is electric, so if the problem would be in it, I assume it would throw some code on me, but there is no MIL or any codes stored. Thermostat might be the issue, which make sense about losing heat while idling (coolant runs on long circle, therefore doesn't warm up well enough to keep the heat), but overheat light don't make sense in this case if the "stuck open" thermostat. Anyone any suggestions? Or maybe someone had similar issue with their Prius? So far the only logical explanation for me is "glitching" thermostat that gets stuck sometimes in "open" position, sometimes in "closed". So I call for wisdom of Prius Gurus on this forum to identify the issue :)
     
  2. BiomedO1

    BiomedO1 Senior Member

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    Location:
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    Vehicle:
    2021 Prius Prime
    Model:
    LE
    I would guess intermittent electric water pump. The impeller is probably loose and getting hung-up once in a while. No pump, no coolant flow, intermittent over temp lamp. This would also explain why you get cold air at a stop light. I doubt you were able to remove all the heat from the engine block at a stop light; but if you coolant pump stopped circulating coolant - you can extract all the heat from the small amount of coolant in the heater coil. The electric motor continues to rotate, so no CEL; but the impeller isn't moving the amount of coolant it should.

    Hope this helps...
     
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  3. Brian1954

    Brian1954 Senior Member

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    Location:
    South Central PA, USA
    Vehicle:
    2011 Prius
    Model:
    III
    How many miles on your Prius?

    Are you the original owner of the car and was the water pump ever replaced?

    I agree that it might be an intermittent water pump.

    Posted via the PriusChat mobile app.
     
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  4. DannyK

    DannyK New Member

    Joined:
    Mar 13, 2022
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    Location:
    Virginia
    Vehicle:
    2010 Prius
    Model:
    Three
    Around 200K on a clock, second owner, got it at 180K 5 years ago (my parent's-in-law car, so they don't drive it much). First owner was religious with capital "R" about maintenance on this car, kept literally all records from day one, but there are no records about water pump whatsoever, so I assume he never had issues with it.

    After talking in details with dad-in-law (he had second occurrence of overheat light) I found out that heat disappeared while driving and after another ~5min of driving he also got "overheat light" on. By the time he made a turn to a parking lot and prepared to stop and shot off the engine - light went off and heat came back after short period of time. He kept driving and light never came back and heater worked normally. Which eliminates the thermostat version completely (that is not how it fails) and give more reasons to believe that intermittently coolant stopped circulating in the system, which probably caused by stuck water pump impeller (considering the mileage on this car). Looks like I'll be on a hunt for a new water pump. I'll update you after pulling the old one to see if we were right. Thanks.
     
  5. CR94

    CR94 Senior Member

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    Location:
    Northwestern S.C.
    Vehicle:
    2011 Prius
    Model:
    Two
    Is the engine coolant level stable, or dropping?
     
  6. Brian1954

    Brian1954 Senior Member

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    Location:
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    Vehicle:
    2011 Prius
    Model:
    III
    I recommend that you buy an OEM water pump. They are expensive, but it beats buying a cheap aftermarket water pump that you may have problems with in the near future. Do the job the correct way the first time. It will save you time in the long run.

    Also, this would be a good time to replace the thermostat and coolant.

    Posted via the PriusChat mobile app.
     
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