90 4.5 exhaust manifold threads
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HT4100 4.1, 4.5, 4.9 Discussion, 90 4.5 exhaust manifold threads in Cadillac Engine Technical Discussion; I've got a check valve leaking on the AIR pipe that runs from the front exhaust manifold to the diverter ...
  1. #1
    drewsdeville is offline Cadillac Owners Master
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    90 4.5 exhaust manifold threads

    I've got a check valve leaking on the AIR pipe that runs from the front exhaust manifold to the diverter valve, allowing exhaust through the valve and giving me grief.

    I'll run out to the junkyard in a few weeks to pick a new pipe up since it's been mangled, the check valve I can get new. But in the meantime I'd like to remove the pipe and plug the exhaust manifold.

    I'm wondering if anyone knows the thread size here.

    I pulled the pipe off and it looks like pipe thread to me, 5/8ths or so. Anyone know for sure?

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  3. #2
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 90 4.5 exhaust manifold threads

    3/8" NPT. I've got one in there now. I bought the kind that is hollowed out on the inside because I was afraid the plug would expand and crack the manifold. I also used a bit of orange/copper RTV to seal the threads.

  4. #3
    drewsdeville is offline Cadillac Owners Master
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    Re: 90 4.5 exhaust manifold threads

    Cool thanks.

    digging through my junkpile, looks like I have one here. It's even hollowed. However, it's brass...I wonder if it can take the high temps.

  5. #4
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 90 4.5 exhaust manifold threads

    Sure can. Mine is brass and has lasted a looong time. Forget about teflon tape though.... the only thread sealant I could find that can take the heat is copper RTV and even that is a stretch.

  6. #5
    drewsdeville is offline Cadillac Owners Master
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    Re: 90 4.5 exhaust manifold threads

    Sweet thanks for the info man.

    I'll probably just thread it in there without any sealant for now. Maybe just a dab of never-seize instead so I can be assured the swap will be quick when I get the parts. It's only temporary...just a week or two.

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