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1996 MPI 454 engine block drain plug question

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  • 1996 MPI 454 engine block drain plug question

    Hello All first time poster and tried to search for this as I am sure I am not the first to ask. I got a new used boat with a mercruiser 1996 454 mpi. I had it winterize professionally which I use that term loosely as they didn’t put all the plugs in. Got in the back country and she was leaking like a sieve on startup. Looked on the starboard engine block and it’s missing a drain plug. It looked to be 3/8” and I had a steel 1/2” that did not fit. My neighbor had a 3/8” blue plastic drain plug and that fit in. I looked online at the parts break down for my motor and it shows first using a bushing that I could not see any dimension information online but looks like it goes 3/8” into block to 1/2” then using a 1/2” plastic drain plug. Is there any issue with just using the 3/8” right into the block?

  • #2
    Usually there is a 1/4" NPT (3/8") reducer and then a 1/8" NPT plug (Items #3 & #4) , but just a 1/4" NPT plug will do in a pinch.

    Alternatively there is the reducer with the blue plastic plug ( items #5,6,7)

    I'd get the correct reducer and plug on order though . . . Might be able to get them at an auto parts store ( GM 454 drain plug and reducer)


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    Best regards, Ted . . . . Cape Cod, MA

    Current Boats: Formula 330 Sun Sport, O'Day Mariner Sail #3224, Sunfish
    Past Boats: Catalina 22 Sail #10531, Formula 242 Sun Sport
    Twin Mercruiser 7.4 LX MPI (0F802036, 039), Bravo 3's (0F806198, 199), Mercury 7.5 HP (1969), Johnson 4.5 HP (1980)

    My Boating Web Pages: http://www.tpenfield.com

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    • #3
      Thanks and I saw a post on your boat with two 454 that is some juice.

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      • #4
        Usually there is a 1/4" NPT (3/8") reducer
        Ayuh,..... I skip all that madness, 'n use plain ole 1/4" brass pipe plugs from my local hardware store,......

        Makes it easier to dig all the crud outa the hole when drianin' the block,....

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        • #5
          Suggestion here: Dip your toe in boat DIY by doing your own winterization. It is quite simple, saves you a bundle, and gives you the confidence that it is done correctly.

          Remove these drain plugs and poke the holes to remove sand/crud to get a complete drain.
          Remove the exhaust manifold plugs to drain.
          Disconnect the water supply hose at the power steering cooler to drain.
          Disconnect the recirculating hose at the recirc water pump to drain.
          Button everything back up and you are ready for summer.
          < 1 hour including beer breaks.

          ...doesn't hurt to remove the battery and store indoors, especially if it gets very cold in winter.
          '96 Larson 174 SEI BR. 4.3LX 4 bbl Weber s/n 0F786604. Alpha One Gen II s/n 0F709315

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          • #6
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            Thanks I think I will do that next fall

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