Black waxy sludge in coolant

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@SteveSRT8, I'm not blaming Dexcool so much as I am blaming neglect from prior owners. This is 13 years and 200k miles without any fluid change. Way out of spec.

@Dave9

In all the posts I've seen elsewhere online, nobody has mentioned black or waxy. To your point, I am not the only person who has ever had a coolant system go without maintenance for too long, so why was I not finding similar situations? Rusty or orange/brown color, goopy (not waxy) sludge, yes, but not black and waxy. So I had to really dig. Not trying to make a mountain out of a molehill, but trying to understand what the heck happened here and how to resolve. The off-the-shelf solutions (chems, and flush kits), youtube examples, and even PRO shops cannot properly flush this thing, so it left me with a sufficient puzzle that I posted here.

"If hot water and detergent cuts the sludge, you have your solution" - how so? No. Flushing jobs are not run when HOT. Yes, you can run the engine with detergent, or some other chem flush, BUT that only breaks things up. You still have to get that crap OUT, and the only 2 ways to do that are: 1) Drain, 2) flush it with a hose (or some other NOT HEATED water source). Draining doesn't get EVERYTHING out, especially when you learn that the junk floating at the top sticks to the walls on its way out when it hits air, so a fluid flush is mandatory. But flushing cools it down and solidifies everything, defeating the whole process. Also flushing the hot crap out with cold water risks cracking your block (already a risk with a chevy 5.3L), so there's all that excitement too.

MY Flush Strategy

This seems to actually work for a severely neglected coolant system.

Disconnect radiator top and bottom hoses and put a sump pump in metal bucket in it's place in the circuit (custom hose attachments made from plumbing parts). Put a super strong magnet at the bottom of the bucket (on the outside is best) to collect iron. Heat the bucket with a propane stove, but not too hot as to kill the sump pump (at least 120F is what I was going for). Throw in a chemical agent of choice (Prestone radiator flush, dishwasher detergent, whatever). Run the engine every hour or so to get fluid up into the heater core (the one place it wont go without the engines water pump turning). OR, pull the heater core hoses and flush it separately.

Btw, I found that a 1/4 hp sump pump using 3/4" pipe produced 9psi on the system, perfectly safe for the system.

Again, even a PRO radiator shop will not do it this thorough or effectively. My shop wanted $700 to do the job with no heat, no sump, and only spend a few hours and result in hardly any of the actual grime to be removed. This will take heat, MANY cycles, many hours, many days to accomplish.


So far, I have done 3 complete cycles of 4+ hours churn through the sump each, and the water is so black I can't even see my fingers 1 inch deep in the water. This - even on the 3rd fresh water swap and repeat! This is soooo bad. Oh, and the magnet consistently has a heap of iron on it that also hasn't reduced in magnitude yet.


I also tried hooking a water hose (COLD, and full of adverse minerals - hard water) and literally flushing the system (not cycle via sump). If forces my heated black water out, and immediately becomes CLEAR. You would think problem solved, right? It's clear, all flushed! But then I hook the sump pump up again, get the heat going and a little prestone or detergent, and POOF, the water goes black as sin. So yeah, don't tell me that typical flush methods resolve this. "Just flush the thing and be done already". Nope, nope and nope. Not that simple. Really frustrating.

I hope to have clear water in the sump one day this week. We'll see. I bought a new radiator BTW (so the black I described above is only coming from the engine cavity and heater core), will be cutting open my old radiator and posting a pic.
 
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Wow. Lucky you, you got that "one in a million" car with a unique problem. Sounds like you have it on the run, my best wishes for a successful cleaning!
 
Originally Posted by roachslayer
What would cause a wax like residue to coat the entire coolant system, reservoir, radiator, engine, etc? I've got a black waxy residue that will not flush out.

Another interesting characteristic is that the solidified residue liquifies when heated and floats to the top like oil. But goes solid again when cooled.

A significant factor: 200k miles, coolant probably never been flushed, aged Dexcool here in a 2006 Chevy 5.3l suburban.

I've identified these possibilities:
  • Burnt oil (head gasket leak)
  • Dexcool mixed with air and/or other contaminant
  • Dexcool eating at gaskets and seals


The problem with the head gasket theory is that compression, leak down and block tests all pass! No signs of combustion gasses getting into coolant. That said, I can't rule this out completely... perhaps it's a small leak that only happen under load?

I've never thought of oil becoming wax, but then again, I also don't understand Dexcool chemistry. But then I learned that overheated oil actually does solidify, also known as engine sludge that can build up in the case due to being burnt. But never heard of this building up in the coolant! Unless perhaps it's literally burnt and accumulating slowly over a long period of time through an undetectable head leak, now completely overtaking the coolant system.

Anyway, I'm frustrated. Even if my head gasket is fine, the engine is doomed as there is no way to get this crap out. Not even a radiator specialty shop offers a heated flush, which is is the only way this junk will ever have a possibility of leaving the system!

Anyone else ever seen anything like this? Ideas ?

Death Cool coolant, faulty head gasket, neglect, to name a few.
 
Sounds like the black Bar's Stop Leak Pellets at work.

There is nothing like what you have been describing that can form on it's own in a cooling system. I've dealt with some so bad and neglected that holes were eaten through cooling system components.

Black goo that migrates only under heat, and immediately attaches itself when cooled or exposed to air?

[Linked Image]
 
I have a 2006 Escalade. Same system same coolant as you. Sealed at the resevoir. No issues. Just staining. I don't think any coolant is good for plastic so I can't blame it for the heater core quick connects failing I think that's just a bad design. Changed once at 120k but it could have gone further. So whatever is going on has nothing to do with Dexcool. It's possible one of the hoses or the plastic is failing have you ever had problems with the quick connects? Do any of the hoses look like they've been replaced?. And lastly are you going through a lot of oil
 
Quick update for any future readers looking at this thread.

@LeakySeals, the hoses were in terrible, degraded shape. Main hose would collapse after cool down. All hoses were nasty on the inside. All looked to be original, never replaced, 200k miles. And like I said, the coolant also looks like it was never replaced in all those miles. No, the vehicle was not going through a lot of oil, had no head gasket leak, oil and coolant were both tested by a lab, oil in perfect shape, water showed signs of metal contaminant (not oil), which the lab suggested was due to age (circulating in engine cavity and pump, never been changed in 200k miles).

I have replaced EVERY aspect of the coolant system (literally, including the engine itself!), except the heater cores (front and rear). Just too much work to yank those. I tried HEATED flush for many hours on them as mentioned here using a sump system.

All new engine (it had non-coolant related issues, loss of oil pressure), all new hoses (every single one of them), all new quick connectors, all new reservoir, new water pump, all new radiator, new T-stat, all new coolant (complete 100% flush), of course.

To my utter disappointment (but not surprise at all), as soon as I put this all back together, warmed up the engine, I immediately saw my brand new reservoir become blackened with the crap coming out of the heater cores.
frown.gif
. All this expense, all that time, all that massive amount of direct flushing of the cores, and still insufficient, no love. In fact, I'm sure my brand new radiator is now partially blocked again with this black sticky sooty crap. The ONLY good news is that I think I flushed enough (or eliminated enough by pulling old radiator, etc) that it's not degraded enough to be an issue, for the time being. Did a trip hauling a trailer, temp raised on the mountain passes when hauling 80MPH up hill, but no overheat.

Conclusion:
@DoubleWasp above might be right about StopLeak being added by the prior owner. "Black goo that migrates only under heat, and immediately attaches itself when cooled or exposed to air" - EXACTLY. The only other significant factors here are the lack of maintenance of hoses and coolant by the prior owner with over 200k miles and no service.

Lesson: ALWAYS check coolant before buying used. Followed by Always replace coolant after buying used.
 
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