Possible Head Gasket or EGR Concerns

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by PriuSocal, Jan 14, 2026 at 12:24 AM.

  1. PriuSocal

    PriuSocal Member

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    I am looking at buying a 3rd gen and came across one today that had the startup “rattle” then goes away 5 seconds later. I looked at quite a few videos including the car care nut’s videos on diagnosing and isolating but no videos talk about CEL codes appearing with either HG or EGR symptoms.

    The car is a 2010 with 197k. The oil looked brownish, coolant looked full but cant rely on that as owner may be topping off. When scanning for codes, I got the following: P0300, P0302, P0303, P0304 codes. I personally witnessed the rattle at startup 3-4 times I started the car. Then its smooth. I have not performed the EGR / Putty knife test yet as I didn't want to get deep into the diagnosis as If it ends up being that the owner may decide to not sell it and i'm not there to help diagnose lol.

    So my question is, would the misfire codes show up on both EGR and HG failures? Or only one of them or none or in both?

    Any help would help as price is an as is sale for $2k.
     
    #1 PriuSocal, Jan 14, 2026 at 12:24 AM
  2. rjparker

    rjparker Tu Humilde Sirviente

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    Its a guaranteed head gasket problem and advanced at that. Which means it very likely needs an engine not just a $2,500 head gasket.

    Considering it could be due for a brake booster and hybrid battery very soon, you should run. Could cost you $5k-$10k in repairs.
     
    #2 rjparker, Jan 14, 2026 at 12:53 AM
    Mendel Leisk likes this.
  3. PriuSocal

    PriuSocal Member

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    Could you elaborate on why it wouldn't be just an EGR issue or just a HG issue or both, but adding it needing a whole new engine? Perhaps if engine is continually being driven with a HG issue, then I agree. I did see in another post titled "Death Rattle" by AncillaryRedoubt you state this:

    "With a head gasket problem you won't get codes because the misfire does not last long enough. Which basically eliminates bad plugs, coils and injectors. This scenario virtually confirms a head gasket problem."

    So I'm a bit confused at the diagnosis at that since this car has misfire codes. Also, I wrench on my own cars so at least save the labor part and those outlandish prices wouldn't apply to me. The more I see other videos the more I see similar issues to mine with different results which is why I'll be putting a borescope into the cyl to see for signs of seepage or washout and if a HG, at $2k may be worth buying and parting out lol.

    Also, Booster is ok and HV battery was replaced 40k ago, He had the receipts from the dealer.
     
    #3 PriuSocal, Jan 14, 2026 at 1:05 AM
    Last edited: Jan 14, 2026 at 5:10 AM
  4. rjparker

    rjparker Tu Humilde Sirviente

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    Most early stage gen3 hg leaks quickly seal when the cylinder warms up masking misfire codes. The guy is selling it as is for $2k.
     
    #4 rjparker, Jan 14, 2026 at 8:16 AM
  5. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Could have a stop-leak product in the coolant too.

    Runaway oil consumption is another factor: until partway through model year 2014, Toyota used piston rings with less outward spring (to reduce friction, get more mpg brownie points), which have proven prone to excessive oil consumption.

    if you want a project, this is the car for you. Lowball the seller though.
     
    #5 Mendel Leisk, Jan 14, 2026 at 8:27 AM
    Last edited: Jan 14, 2026 at 8:33 AM
  6. RavenPri

    RavenPri New Member

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    So where is this located? I'll take it for 2k. If you have the means to fix it yourself its an easy flip. ~1200 for parts and shipping. Easily get 6k.
     

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    #6 RavenPri, Jan 14, 2026 at 1:46 PM
  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    New water pump is probably prudent. Ditto for the head bolts. And of course the engine overhaul gasket kit. But:

    New EGR valve?
    10 spark plugs?
    Various misc gaskets, are they not in the gasket kit? That's the full kit, should be quite complete.

    For a flip, I think gasket kit and head bolts would suffice. Spark plugs, water pump are easy to replace down the road, existing EGR valve I would only replace if it has internal damage. So about $300 USD. :)

    Addendum, the gasket kit and head bolts, from Amayama, all-in, is $282.31 CDN for me, that's $203.43 USD.

    upload_2026-1-14_11-19-5.png

    On the other hand, the cylinder walls could be scored, the damper could have sustained damage, a piston arm might be bent, and so on.
     
    #7 Mendel Leisk, Jan 14, 2026 at 2:11 PM
    Last edited: Jan 14, 2026 at 2:21 PM
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