85 Seville HT4100
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HT4100 4.1, 4.5, 4.9 Discussion, 85 Seville HT4100 in Cadillac Engine Technical Discussion; Hi guys I'm new to the forum and am not that familiar with this engine so please bear with me. ...
  1. #1
    mike57 is offline Cadillac Owners Member
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    85 Seville HT4100

    Hi guys I'm new to the forum and am not that familiar with this engine so please bear with me. I just sprung a collant leak from the right rear (passenger side) of the engine, toward the firewall. If you push the plug wires out of the way you can feel silicone it almost feels like a round plug a few inches below the valve cover. There is definately silicone there as I can get my fingernails under it. It is pissing out a steady stream of coolant just slightly less than someone taking a piss. My thinking is that it might be a freeze out plug and I have the shop manuel for it but can't find a diagram as to where the freeze out plugs are on this engine. I can put my finger over the silicone and this is where the leak is. Does anyone know if there is a freeze out plug in this area? Any help would be greatly appreciated.

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  3. #2
    mike57 is offline Cadillac Owners Member
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    Re: 85 Seville HT4100

    Hey guys I just took a mirror and flashlight out and the coolant is comming out of a tiny porosity hole in the casting itself. I was thinking of cleaning the area off with rubbing alcohol and using epoxy resin. Is this the best way to fix this?

  4. #3
    awadecki is offline Cadillac Owners Enthusiast
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    Re: 85 Seville HT4100

    Never heard of this, but if it is in fact a porosity hole, you can try epoxy resin, or you can peen the aluminum with a dull punch.

  5. #4
    mike57 is offline Cadillac Owners Member
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    Re: 85 Seville HT4100

    Quote Originally Posted by awadecki View Post
    Never heard of this, but if it is in fact a porosity hole, you can try epoxy resin, or you can peen the aluminum with a dull punch.

    I had the car since 1999 and it just sprung the leak. Apparently someone in the past had put silicone over the area because I peeled off the silicone and the coolant is comming from the casting itself. I work in a CNC machine shop and we reject everything with porosity but porosity is not at all uncommon in castings, we get many rejects because of this. We however never attempt to repair such castings, they are considered junk and are sent back to the casting foundry.

  6. #5
    mike57 is offline Cadillac Owners Member
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    Re: 85 Seville HT4100

    I should also note that I have been using bars leak at every coolant change and I have to assume that this is what kept the leak at bay. The silicone that someone put over it in the past should never have held all these years.

  7. #6
    awadecki is offline Cadillac Owners Enthusiast
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    Re: 85 Seville HT4100

    Some HT4100s did have casting porosity problems, but I've never heard of someone who owned one. If the hole is small, I'd try the peening method first.

  8. #7
    carnut is offline Cadillac Owners Master
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    Re: 85 Seville HT4100

    The later factory service manuals talk of this and said to use JB WELD.

  9. #8
    mike57 is offline Cadillac Owners Member
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    Re: 85 Seville HT4100

    I used the peening method then put epoxy over it and it's not leaking so far. A guy at work claims to have sealed a head gasket leak with this product http://www.barsproducts.com/1111.htm It's a new product from Bars Leaks, you don't have to remove the coolant, sounds interesting to prevent future leaks. I called advance auto parts and it's 29.99 so it's seems well worth it if it really works.

  10. #9
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    Edahall is offline Cadillac Owners Enthusiast
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    Re: 85 Seville HT4100

    Quote Originally Posted by mike57 View Post
    I used the peening method then put epoxy over it and it's not leaking so far. A guy at work claims to have sealed a head gasket leak with this product http://www.barsproducts.com/1111.htm It's a new product from Bars Leaks, you don't have to remove the coolant, sounds interesting to prevent future leaks. I called advance auto parts and it's 29.99 so it's seems well worth it if it really works.
    That sounds like a guaranteed way to clog up your heater core. Since it's not leaking with your epoxy fix, just leave it the way it is and drive it.

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