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  1. #1
    Petty Officer 1st Class
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    Default grease or sealant with manifold gaskets?

    94 Crownline with 5.7 MCM Alpha (engine serial #OF281631) - I am replacing the thermostat, exhaust manifold and elbow gaskets. The manual recommends gasket sealant. The parts guy at my boat shop strongly recommended that I use grease instead of sealant. He said that the sealant will cook, become briddle and not form a tight seal with the two surfaces. Which one do you recommend - grease or sealant? Either way, I'm assuming you coat both sides?

  2. #2
    Lieutenant Commander bjcsc's Avatar
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    Default Re: grease or sealant with manifold gaskets?

    Never heard of using grease...manifold gaskets go on dry, riser gaskets vary - some new styles go on dry, some require sealant. Thermostat gaskets use sealant as well.
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  3. #3
    Lieutenant Commander bjcsc's Avatar
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    Default Re: grease or sealant with manifold gaskets?

    And yes you do coat both sides. Permatex Hylomar sealant is an excellent choice and will not harden or dry out.
    Full Gallop
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  4. #4
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: grease or sealant with manifold gaskets?

    The exhaust riser gasket materials changed in 99, so your 93 manual will not reflect that change.
    Here is the Merc service bulletin that came out on which gaskets to use and how to use them.

    Service Bulletin 99-10
    Don S.


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  5. #5
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    Default Re: grease or sealant with manifold gaskets?

    Thanks Don. My Quicksilver elbow gaskets are labeled 27-863724, so it appears per the bulletin that they go on dry. Would you also recommend some grease on the gasket as did the parts guy or does "dry" mean "dry"?

    My two Osco manifold gaskets are labeled "CV-GH" on the box and "CMP-4000" on the gasket. I couldn't find this number on the bulletin. Do you know if they go on dry as well?

    Thanks!

  6. #6
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: grease or sealant with manifold gaskets?

    Would you also recommend some grease on the gasket as did the parts guy or does "dry" mean "dry"?
    Dry means just that, DRY, nothing, no sealer, no grease, nothing, nada.......

    Buy parts from that "PARTS GUY" from now on. Installation procedures is not his strong point.

    I've never dealt with OSCO, so couldn't say what their recommendations are for any of their gaskets.
    Don S.


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  7. #7
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    Default Re: grease or sealant with manifold gaskets?

    For anyone else reading this post, I just found a Tech Bulletin on Osco's website.

    http://www.oscomotors.com/catalog/catalog75.asp

    Osco gaskets should also be installed dry.

  8. #8
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    Default Re: grease or sealant with manifold gaskets?

    I have used and always been told to use the "Aviation Form-a-Gasket". Its brown sticky stuff comes in a short bottle with a brush. Thats what my repair manual said to use on all surfaces even between the engine and manifold. Its made by Permatex i think?

  9. #9
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: grease or sealant with manifold gaskets?

    Quote Originally Posted by wakeboarddude View Post
    I have used and always been told to use the "Aviation Form-a-Gasket". Its brown sticky stuff comes in a short bottle with a brush. Thats what my repair manual said to use on all surfaces even between the engine and manifold. Its made by Permatex i think?

    Then you have been told wrong, and the manuals you are reading are wrong.
    Since every manual can't be changed, that is why Merc uses Service Bulletins. It doesn't help the DIYers, but it does help us dealers keep up with changes.
    The gasket material was changed back in 99. So using any sealer actually does more harm than good. So be careful what you recommend. Now you may know why your gaskets fail so soon.
    Don S.


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  10. #10
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    Default Re: grease or sealant with manifold gaskets?

    So now what do i do? Take it apart and clean the gunk out, or replace the gaskets. I only have a few hours on the boat after putting it all back together. The Gaskets I used are the green Sierra gaskets that came with the new manifold. I used the AViation gasket stuff. Should I be worried or just change them at the end of the season?

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