Intermittent Misfiring with no Overheating

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by AnnaBiJou, Mar 25, 2026 at 9:25 AM.

  1. AnnaBiJou

    AnnaBiJou Junior Member

    Joined:
    Mar 8, 2022
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    Location:
    Willington, CT
    Vehicle:
    2013 Prius v wagon
    Model:
    V
    Hello everyone, I hope you can help me with something pretty serious.

    2012 Prius V, it's been having intermittent random misfires for months on cold starts and rarely on light acceleration. It's suddenly gotten a lot worse, to the point that I'm scared to drive it now, misfiring every time on start up and when the engine engages. The misfires do not last, once it misfires a few times the engine will smooth out. I just got the check engine light and codes which is not helpful, saying random misfire, and misfire on cylinder 1, 2, 3.

    Looking it up and getting a scan gauge 3 to help monitor radiator temp, the highest radiator temp was 201F very briefly, it hangs around 195F on all drives, out of curiosity I checked the cat temp and saw it was 973F, which I do believe is normal temp, both the cat and the radiator. I'm honestly thinking it's the head gasket, despite the lack of common symptoms. The oil was changed recently as well and it's not foamy or high, the radiator fluid is not going down consistently, though has been low a couple times. My dealer has said because there is no overheating, no clouds of white exhaust, and no sign of piston wash, according to them it cannot an issue with the head gasket.

    Going through the car, the dealer replaced the spark plugs, discovered two of the coils are non-OEM, and switched them around to see if that helped anything, it has not. I'm going to be replacing the coils next, I have all of the tools and video guides to do it, I'm just a little nervous to do that, and clean the manifold, which has been another common reason for the misfires from what I've found. I got a second one to clean and swap it out with the one in the car.

    Questions that I have, is there anything else I should be doing before replacing the coils/cleaning the manifold?
    From what I've watched I need to disconnect the two coolant hoses from the throttle body, yet nobody shows or even mentions needing to bleed the coolant system. If an air bubble gets into the system, will it blow the head gasket? How would I bleed the system if that is a concern?

    Any help is greatly appreciated, any answers or any other suggestions as to what else I should do to try and solve this before I jump for a head gasket replacement that may not even fix the problem.​
     
    #1 AnnaBiJou, Mar 25, 2026 at 9:25 AM
  2. BiomedO1

    BiomedO1 Senior Member

    Joined:
    Mar 27, 2021
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    Location:
    SacTown, Ca
    Vehicle:
    2021 Prius Prime
    Model:
    LE
    IMHO; you need to test for head gasket failure; BEFORE throwing parts and extra work at this problem.
    How many miles and how long have you had this car?
    Do you check the fluid levels at every fill-up and has the coolant level been going down?
    Could someone have put stop-leak in the coolant to cover-up this problem and now that 'patch' had fallen off?
    Your dealer doesn't know what they're doing - don't waste your time & money there anymore.
    These cars usually seep coolant into the combustion chamber when engine is cold, which causes a misfire during start-up. When the engine warms-up, the aluminum expands and seals the coolant seepage. That's why your problem is intermittent and only during start-up. The dealership has a TSB on that and should know better!! Did they sell you the car and don't want to repair it under warranty???? Find a Prius specialty shop for proper diagnostics.

    Pull the spark plugs, check the tips and borrow a borescope to check the pistons for steam cleaning.
    You need to do a compression and leak-down test, WHILE the engine is cold. The 'car care nut' YouTube channel has the procedure.
    The different coils is an indication that someone has already tried fixing this problem without proper testing and diagnostics. In other words throwing parts at the problem, hoping to fix it that way. TESTING is the only way to nail-down a problem, rather than blindly throwing parts at it. Those aftermarket coils tells you that someone has already done that and that the problem is persistent..

    Good Luck....
     
    #2 BiomedO1, Mar 25, 2026 at 10:27 AM
    Last edited: Mar 25, 2026 at 11:48 AM
  3. Mendel Leisk

    Mendel Leisk MMX GEN III

    Joined:
    Oct 17, 2010
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    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    What’s the miles and how long have you had it?

    head gasket failure is VERY common 3rd gen and Prius v problem.
     
    #3 Mendel Leisk, Mar 25, 2026 at 11:27 AM
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