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Thread: Blackish Coolant

  1. #1

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    Blackish Coolant

    Last night I drained my radiator and was surprised to see a black tint to the water. No antifreeze in the system yet, only water. I was expecting to see more of a rust color as I have in the past.

    I didn't take a photo, and don't know if there was any oil in it. I dumped it out before my brain thought "that water's black so maybe you should analyze it in the daylight". It's gone.


    It was not a thick black color, but more of a black tint. And I didn't notice any oil appearance either.

    I'm scared to ask, but anyone seen this before?

    Head Gasket? Crack in head?
    Dave
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  2. #2
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    You say you drained water (not antifreeze) and it was discolored and looked like a black tint and there was a lack of rust. My guess is that is aluminum oxide (which is normally black) discoloring the water. Water will cause aluminum parts to corrode and the constituents in tap water usually makes the corrosion worse. The aluminum may act as a sacrificial anode and actually provide some ant-rust protection to the iron parts of the engine (lack of rust in the water) and heat accelerates this chemical reaction. It would have been interesting to capture that water and use a simple pool pH strip and I'll bet it would be acidic.

    Of course if you think there is a chance you have oil in the water causing this condition you need to check the oil for presence of water. If there is lots of emulsified oil in the water you will see it immediately but small amounts don't give that characteristic milky appearance. If the car has not been driven for a few days the water phase will be at the bottom of the pan and draining the oil into a glass jar will show the water phase. A crackle test is an even better way to detect water in oil and is simple to do. A few drops of the suspect oil on a hot plate heated to well above the temp water boils at but below the boiling point of oil and if water is present you will hear the crackle as it instantly turns to steam. But based on your symptoms my first guess is aluminum oxide.

    Flush the system thoroughly and refill with a 50% mixture of antifreeze and pure water (don't use tap water) or you can simply purchase the ready mixed stuff like I do and don't worry about buying distilled water and mixing the proper ratio. Coolant has corrosion inhibitors to prevent galvanic corrosion of the dissimilar metals used on most cars.

  3. #3
    Administrator David Hodgkins's Avatar
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    What he said.

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  4. #4
    Senior Member Avalanche325's Avatar
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    The only time that you should have water only in the system is the very first start, just in case you have a major leak. That is assuming that you fill the system and fire it up immediately. You should then put antifreeze in as soon as it cools down. This is for the corrosion inhibitors.

    As NAZ said, If I were you, I would drain it, flush it until no more black stuff, and then fill with 50 / 50 antifreeze and water.

    Usually oil in the water looks more like foamy tan goo.

  5. #5
    Senior Member cv2065's Avatar
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    I always used distilled water here in Florida to mix with the anti-freeze, as the tap water is very hard and causes scale. If you mix it separately, you can get a dilution scale at a local automotive store to ensure you get the right 50/50 mixture. Or, you can get the pre-mixed and good to go there as well, just costs a little more.
    Last edited by cv2065; 05-16-2018 at 04:34 PM.

  6. #6
    Senior Member rich grsc's Avatar
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    There is no need to use a 50/50 mixture if you live in a warm winter state, 30% is enough. As others have said, the result of using water with no corrosion additives, it'll be fine.

  7. #7

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    During my radiator debacle, I drained more of the water out and it was the rusty color that I had expected in the first place. There's the thinnest sheen on the surface, but no oil in the mixture.

    2018-05-19_01-34-23 by D. R., on Flickr

    I'll be putting in a coolant mixture on the next fill
    Dave
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  8. #8
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    I you have a pool supply nearby or Lowes or Home Depot; pick up some pool pH test strips and check the pH of the water you drained from your cooling system. I think you'll find it's far below the ideal range of between 9.5 & 10.0 pH. A pH of 8.3 or lower is corrosive to your system. Pure water is 7.0 pH and considered neutral (not acid or base) but that's actually corrosive to an iron block and aluminum radiator.

    One more reason why running straight water is a bad idea for automotive cooling systems.

  9. #9
    RoadRacer's Avatar
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    Quote Originally Posted by NAZ View Post
    the ideal range of between 9.5 & 10.0 pH
    fascinating, never heard this before. I'm a pool testing fanatic so I tested my 50/50 coolant mixture.. there was no free chlorine Alkanity and pH were off the chart, i.e. 240+ and 9+ respectively. Neither strips nor my 'proper' FAS-DPD kit go high enough for your numbers though..
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  10. #10
    Senior Member Fixit's Avatar
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    Just flush it out, buy a few gallons of 50/50 pre-mix, and be done with it.
    (Between galvanic reaction of riv-nuts, and pH levels of anti-freeze water this is getting rediculous!)
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  11. #11
    Senior Member cv2065's Avatar
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    You can get yourself a radiator flushing kit at your local auto parts which will flush the block out as well.

  12. #12


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    Jeff Kleiner's Avatar
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    Quote Originally Posted by Fixit View Post
    Just flush it out, buy a few gallons of 50/50 pre-mix, and be done with it.
    (Between galvanic reaction of riv-nuts, and pH levels of anti-freeze water this is getting rediculous!)
    THANK YOU!

    Jeff

  13. #13
    Senior Member rich grsc's Avatar
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    Quote Originally Posted by Fixit View Post
    Just flush it out, buy a few gallons of 50/50 pre-mix, and be done with it.
    (Between galvanic reaction of riv-nuts, and pH levels of anti-freeze water this is getting rediculous!)
    Exactly

  14. #14
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    Fill the system run it for a good 10-20 miles let it cool then drain and refill. Then your done. You probably have a decent amount of build up in the system. Some higher engine speeds will help flush things out. If you want to flush it that is also a option.
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  15. #15
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    One additional possibility, although somewhat remote. (The previous postings are spot on and cover the 90%+ probabilities.)

    However, another potential remains. We are all familiar with the symptoms of a blown head gasket that allows oil to get into the water, or vice-versa. On some engines, you can blow a gasket that separates the exhaust gas from the coolant. In this situation you will not see anything unusual in the oil. Nor will you see the typical symptoms of oil in the water. What you will see is black desolved exhaust soot in the water or clinging to the sides of the overflow tank.

    Not likely you have this situation, but you should be aware, if the above mentioned suggestions don’t cure your problem.

    A pressure test of the cooling system will give the answer.

  16. #16
    Member Frank Messina's Avatar
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    Luckily, not having to be concerned about freezing temps, I have only run distilled water and Water Wetter. 26,000 miles and two changes since first fill. Works great.
    Frank
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