Overheating issue?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Detrixnmeemoo, Oct 28, 2025 at 6:23 PM.

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  1. Detrixnmeemoo

    Detrixnmeemoo New Member

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    2010 Prius
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    My check engine light is on, and my thermostat light will come on while on hills and highway, but flashes then shuts off once my foot is off the gas. I have a little rough start up on cold mornings (being my mornings are 35°F) it sounded like the spark plugs were going, so I replaced those and the coil packs. I still get a rough start but it's fine after a few seconds. Now my temp light comes on every now and then. Which obviously freaks me out until I notice it shut off when I release the gas pedal. Took it to a mechanic who used to work at Toyota and said I need a new heater exchange which I can't find online. Is he wrong or am I not looking for the correct part?
     
    #1 Detrixnmeemoo, Oct 28, 2025 at 6:23 PM
  2. Brian1954

    Brian1954 Senior Member

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    It sounds to me that you may have two separate problems.

    If the check engine light is on, you need to use a scanner to read the trouble codes. The trouble codes will narrow down the problem that the car is having.

    The overheating of the engine may be caused by an engine water pump that is going bad. The water pump is not spinning fast enough to cool the engine. If you only have the engine overheat warning light come on during high throttle usage, and the warning light turns off when you easy off the throttle, then I am guessing that you need to replace the engine water pump ASAP.

    The rough cold start of the engine could be the beginning of a bad head gasket. Coolant is seeping past the head gasket into one of the cylinders in the engine. It is typical in this engine for this to occur in cylinder #1 or #2. You need to mark the level of the engine coolant on the engine coolant reservoir and check it often.

    How mile miles on your Prius?

    Edit: Where is PA do you live. If you are close to me, I may be able to help.
     
    #2 Brian1954, Oct 29, 2025 at 9:38 AM
    Last edited: Oct 29, 2025 at 2:13 PM
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  3. BiomedO1

    BiomedO1 Senior Member

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    You'll also have to keep an eye on your coolant levels, since it may be leaking into your combustion chamber. If your temperature lamp is coming on more often - your likely doing damage to your engine.
    Look up common gen3 engine problems.
     
    #3 BiomedO1, Oct 29, 2025 at 10:47 AM
  4. bisco

    bisco cookie crumbler

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    how many miles on her?

    is the heat exchanger at the exhaust system?
     
    #4 bisco, Oct 29, 2025 at 1:58 PM
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