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Catalytic Converter Gasket Question

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Sam Brinson, Jul 21, 2022.

  1. Sam Brinson

    Sam Brinson Junior Member

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    Hello. Putting a new cat on my 2008 and I had a quick question.

    With regard to the gasket that goes between the catalytic converter and the exhaust manifold, is there any harm to using exhaust gasket-maker sealant to attach it to the catalytic converter, before installing the cat?

    I am in the middle of this project, and am planning on re-attempting to put the cat in this evening (after some new bolts come in the mail, long story), but I remember the last time, I had a difficult time in keeping the gasket properly positioned when putting the cat into the exhaust manifold. Would be much simpler to just glue it onto the cat, if that wouldn't present an issue.

    Thanks for any info.
     
    #1 Sam Brinson, Jul 21, 2022
  2. Tombukt2

    Tombukt2 Senior Member

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    That should be a round fiber washer with spring bolts it has to. BE able to swing 20 or so degrees . I believe . Read gasket makers text on tube . Nope . The gasket w bolts n springs only costs 25 bux at best . Came with my cheap e bay converter.
     
    #2 Tombukt2, Jul 21, 2022
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  3. mr_guy_mann

    mr_guy_mann Senior Member

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    If you wanted to try high temperature exhaust sealant of any kind, I would try to "glue" the gasket to the manifold. There is no movement between the gasket and the manifold. The gasket is designed to slip some in the cat pipe (a ball and socket joint).

    Side note, I only use a donut gasket from Toyota as most any other brand will usually have some leaks at that joint. Period. The Toyota gasket seals great, even with most AM cat assemblies. Also I don't have any problems just pushing a Toyota gasket onto the manifold stub pipe and having it stay put.

    Posted via the PriusChat mobile app.
     
    #3 mr_guy_mann, Jul 21, 2022
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  4. PriusCamper

    PriusCamper Senior Member

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    Biggest problem with hi-temp gasket sealant is it gives off really nasty smelling toxic fumes once it heats up. I used it on my first cat swap, but never again. The main challenge with these leaking is if the cat gets clogged, or if there's not enough pressure holding it in place via the spring bolts. Sometimes when the aftermarket cat is a bit short it can counter act the very weak spring pressure on that seal. For best results the rubber mounts that hold the resonator should be angled back slightly so they assist in pulling the cat towards that seal.
     
    #4 PriusCamper, Jul 21, 2022
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  5. edthefox5

    edthefox5 Senior Member

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    Quite a big void there to fill with goop and a waste of time imho. That's a critical seal there if even a tiny leak you will smell exhaust in the cabin.

    Go buy a brand new toyota donut.
     

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    #5 edthefox5, Jul 22, 2022
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  6. Sam Brinson

    Sam Brinson Junior Member

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    I bought an OEM gasket and as mr_guy_mann suggested, it stuck on without the need of sealant. I think the aftermarket one I tried before was the problem. Thank you all for the help. Cat is finally installed and all is well.

    It was a hell of a job, with a broken off bolt in the exhaust manifold, but all is well. In case anybody ever comes across this post when googling, I'll explain how the broken bolt issue was dealt with. I couldn't tap it out with a bolt extractor, as it was stuck in too solidly. Ended up drilling it out (3/8") and using new extra long bolts (M10x1.25x100, fully threaded) ordered from Belmetric and 4 M10x1.25 nuts. Would suggest buying a couple of these and using the bolt covers/spacers on both sides of the exhaust manifold/cat joint, as the nut on the exhaust manifold cannot be effectively tightened due to space limitations from the OEM manifold's built in threaded guide for the bolts. And remember to use 2 nuts on each side, so that they lock together and don't come loose. It's a minor expense, money-wise and time-wise, compared to replacing the exhaust manifold, in case a bolt becomes broken off in it, or if the OEM threading on the manifold becomes unusable. (I had broken threading on one side, and a broken bolt on the other. You can probably just do this on one side, but I cannot confirm as I have not tried)
     
    #6 Sam Brinson, Jul 22, 2022
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  7. edthefox5

    edthefox5 Senior Member

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    I bought an aftermarket G2 cat on amazon. Worked perfect but the donut that came with it was not even close to the size needed.

    Bought a new donut cat was perfect. And no check engine light.
     
    #7 edthefox5, Jul 22, 2022
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  8. Tombukt2

    Tombukt2 Senior Member

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    Usually the check engine light takes a few minutes or a little while to show up I'm thinking it's because folks rarely change the upper O2 sensor The downstream when is easy to change and get at the upper one well it's a little more of a challenge and I can see where people would leave it forever I'm thinking in my '09 when I get a fresh one in the bottom and the top my aftermarket cat will then keep the light off them pretty much bedding because there's nothing else in the system I can't imagine a cheap cat would cause a low threshold problem which essentially means some kind of a flow issue a new cat even a crappy one should have plenty of flow now how fast it clogs up is another story
     
    #8 Tombukt2, Jul 22, 2022
  9. mr_guy_mann

    mr_guy_mann Senior Member

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    OR, maybe a cheap cat doesn't have as much precious metal in it as a $$$ cat. Toyota uses Oxygen Storage Capacity test for the cat monitor. If the new cat doesn't have enough cerium in it to store oxygen like the OE cat does- it will fail and throw P0420.

    Or it could be a small exhaust leak throwing off either sensor. Or either sensor could be bad- esp cheap replacements. Or if the engine burns lots of oil that can coat the cat brick fairly quickly- oil can "kill" the cat without causing it to clog up.

    Could be lots of things.


    Posted via the PriusChat mobile app.
     
    #9 mr_guy_mann, Jul 24, 2022
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