Question about the Thermostat Light

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by GlitterPsycho, Feb 6, 2026 at 10:02 PM.

  1. GlitterPsycho

    GlitterPsycho Junior Member

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    So I’ve been having some issues with my 2013. In August, the EGR valve said it was clogged so i had it cleaned. The light came back on at the end of December and i had it cleaned again because i don’t want a car payment. It came back on two weeks later and he said the intake manifold was also dirty so he took that apart and cleaned it and replaced the seal. During this whole time, it never ran rough or anything, it was just throwing the emission codes. Today i was driving and the thermostat light flashed red for about five seconds maybe and then turned off. I pulled over and waited a bit and it didn’t come back on when i started it. I read online that maybe it can be from air bubbles getting trapped when the intake is cleaned. Is there any truth to this? Do you think it’s drivable? Or do i need to take it back to the mechanic? I really, really, really do not want a car payment but i also don’t want to keep investing too much. I replaced the engine like three years ago and the water pump at the same time. Is it worth it to keep paying more?
     
    #1 GlitterPsycho, Feb 6, 2026 at 10:02 PM
  2. indel

    indel Member

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    What is the mileage on the car? Have you ever had the thermostat replaced? This would be a good time to replace both the water pump and the thermostat. Both are diy jobs if you are handy.
     
    #2 indel, Feb 7, 2026 at 8:41 AM
  3. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Some backstory.

    any chance your mechanic put a stop-leak product in the engine coolant?


    What’s the rate of oil consumption?
     
    #3 Mendel Leisk, Feb 7, 2026 at 9:41 AM
  4. Brian1954

    Brian1954 Senior Member

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    Please list all the trouble codes your car presently has.

    Removing and cleaning the intake manifold does not require any coolant hoses to be removed, so there is no way for air bubbles to get into the coolant system.

    When the water pump was replaced three years ago, was a new Toyota OEM pump used, or was the pump an aftermarket?

    The red engine coolant temperature light is turned on when the coolant reaches 248F. One possibility is that the water pump is going bad. To diagnose this, use a scanner to monitor the engine coolant temperature while you drive the car. Normal coolant temperature is 185 to 201F.
     
    #4 Brian1954, Feb 7, 2026 at 10:58 AM
  5. ChapmanF

    ChapmanF Senior Member

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    There isn't really a code that says the EGR valve is clogged. There is a P0401 code that says a self-test for EGR flow saw a low value, which suggests there is clogging somewhere in the EGR system (unless it's a valve that's not opening enough, perhaps because of a rutted ski jump, or something interfered with the test and messed up the result).

    How's the coolant level?
     
    #5 ChapmanF, Feb 7, 2026 at 11:13 AM
  6. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Agree, but a lot unnecessary disconnection of the throttle body coolant hoses does happen. @NutzAboutBolts intake manifold cleaning video doesn't help matters:

     
    #6 Mendel Leisk, Feb 7, 2026 at 11:49 AM
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