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Thread: Freeze plug sealant

  1. #1
    Registered User
    Join Date
    Apr 2002
    Jacksonville, FL

    Freeze plug sealant

    I've been running searches on what to use to seal a freeze plug with. The only info I found was to use locktite on one post.

    Is locktite what most members have used to seal freeze plugs with?

  2. #2
    Club Member Derek's Avatar
    Join Date
    Jun 2007
    Wiltshire, England
    You shouldn't need to seal them with anything to get a waterproof seal - If one is leaking, I would replace them all as they may be corroded on the inside.

    Changing them is quite fiddly, at least when the engine is in the car -the biggest problem is finding room for your hands and tools. I replaced mine with the engine out (see pic)

    First remove the leaking plug,

    There are a number of ways of doing this. The two most common ways are;-

    Using a small, sharp cold chisel make a slot in the plug, insert the blade of a screwdriver in the slot and lever the plug out. .


    Drill a 1/4 (ish) diameter hole in the plug and insert the tip of a pointed screwdriver into the hole and lever out.

    The plug sits on a locating ledge inside the hole

    The sides of the hole and the ledge need to be scraped clean (file tang/wire brush etc) to provide a clean surface for the new plug to seat on. Make sure that corrosion has not enlarged the hole which could lead to the standard core plug being too small. If the core plug simply drops into place beware!

    Whilst its not strictly necessary I usually apply a light coating of jointing compound around the inside of the hole before I place the new core plug in position.

    Place the new plug, DOME UPWARDS, into the hole and GENTLY tap the plug down so that it is seating squarely on the ledge.

    Select a suitable steel/ aluminium/ brass drift, of approximately the same diameter as the core plug (a socket would be ideal).

    Position it squarely on top of plug and using a heavy hammer hit the top of the drift with a single firm blow. This will cause the plug to spread and grip the sides of the hole. Do not use a series of light blows or keep hitting it with a heavy hammer! If you do your new plug will almost certainly leak or fallout! You have been warned!

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    1961 190SL (DB180 Silbergrau metallic / Blue interior 121040-20-020378)
    1992 300SL (R129 LHD) (Now down in her 'new home' in sunny Spain)
    2005 SL55 AMG (The play thing)
    1936 MG-TA (the current project)
    2004 Jaguar XJR (The daily driver)

  3. #3
    There are stainless plugs now available. Be sure to ask for these when buying them as there are a lot of the old plugs still out there.

  4. #4
    of the West Walter's Avatar
    Join Date
    Sep 2003
    San Diego
    There are two styles of plugs.

    Screw in and press in.

    On the later, screw in ones, you need a new aluminum washer.

    The press in ones, I always used a big socket to press them in with.

    On all things water related I always used non hardening Permatex sealer.

    EVERYTHING gets that Permatex and they always can be taken apart later.

    EVERYTHING that contacts the cooling water. Bolts, hoses, fittings, everything. It never gets hard and seals. The parts are always easy to take apart later. Pure Magic. Love it.
    Walt in the West says: Don't ask: "Use the SEARCH Luke"
    1959 190SL DB050 with 333 leather blue ("It's Alive!" - 653 miles) Chassis 14445
    1961 300SL Roadster DB608 with red - fresh brakes and rebuilt engine hung in - more work coming!

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