Brown sludge?
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HT4100 4.1, 4.5, 4.9 Discussion, Brown sludge? in Cadillac Engine Technical Discussion; While replacing my water pump i noticed some brown sludge line my radiator over flow tank. Any one know what ...
  1. #1
    BLMDeville is offline Cadillac Owners Fanatic
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    Brown sludge?

    While replacing my water pump i noticed some brown sludge line my radiator over flow tank.

    Any one know what it is and what might cause it?

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  3. #2
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: Brown sludge?

    It might be the stop leak dumped in it over the years. I have heard GM does not recommend using it anymore, although they still sell it. Make sure the small hose from the radiator to the reservoir isn't plugged. I take mine off and flush it out best I can if I change the coolant. I'm getting ready to change it out and am going to order a new reservoir this time.

  4. #3
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: Brown sludge?

    I read about this a while back, I forget what it is... I've seen this a number of times even in vehicles that dont take the powder. I believe it has something to do with the coolant vapors condensing inside the tank and forming that brown almost 'foamy' stuff kind of like standing water does in a mud puddle. I dont think you need to worry about it. I usually take the tank out and flush it. I see it more often on vehicles with pressurized tank systems unlike your 4.9's 'overflow' type.

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Brown sludge?

    Yeah, It's most likely sealant tab residue.

  6. #5
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: Brown sludge?

    I'm with Ranger on this. Just now getting close to having most of it flushed from system. I don't think you will ever get rid of it completely, even with a heater core flush.

  7. #6
    83CADMAN's Avatar
    83CADMAN is offline Cadillac Owners Fanatic
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    Re: Brown sludge?

    Just because Caddy does not use it any more doesn’t mean the old cars don’t require it. I allways replace the seal tablets in my 83, HT4100.

  8. #7
    BLMDeville is offline Cadillac Owners Fanatic
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    Where are the seal tablets?

  9. #8
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: Brown sludge?

    You can get them from the stealership. The GM part number is 12378254.

  10. #9
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Brown sludge?

    Quote Originally Posted by BLMDeville View Post
    Where are the seal tablets?
    Where or what? They are Barsleaks tabs (product code HDC). The powdered version is (G12BP). Get them at Walmart, dealer, most parts stores. As for what they are, see the sticky in the Northstar forum.

  11. #10
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: Brown sludge?

    Here's part of the old package I use for a book marker...




  12. #11
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: Brown sludge?

    Here's part of the old package I use for a book marker...


  13. #12
    cadchris's Avatar
    cadchris is offline Cadillac Owners Fanatic
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    Re: Brown sludge?

    Maybe save it and mix it with "Pink Slime" to make a better burger........yeah.......I know.......

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