Heater Core Sludge - Source?
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  1. #1
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    Heater Core Sludge - Source?

    Starting this thread on Heater Core sludge ...since the search is apparently having problems... ( index passatworld_com-threadindex,passatworld_com-threadindex-delta: no such filter attribute 'replycount' ).

    For those of you who've flushed heater cores, what did the "sludge" look like? If you've had an oil/water cooler failure that allowed oil into coolant, indicate this as well. (Is this the cause of sludge?)

    Specifically looking for instances where the heater core formed sludge without ony other apparent failure. Could it be that the metal used to manufacture the HC is causing a slow fouling (sludge build-up on metal surface) regardless of the coolant used?

    Thanks for your responses/opinions.

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  3. #2
    Super Stealth Retired Moderator JayTheSnork's Avatar
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    it isn't sludge. it is flakes of coolant that get lodged in it (pinkish/brownish). there might be a reaction due to disimilar materials in the heater core - looks to be aluminum and something metal that looks bronzish, but definitely isn't bronze, reacting with the coolant.

  4. #3
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    From the one core I flushed out, it looked to be mostly calcium deposits. Car only had OEM fluid and distilled water. I have seen plenty of rust on the inside of the engine block on several 1.8T engines that had only used OEM coolant for 100K or so.

  5. #4
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    The source is the coolant itslef. There may be some outside players, but the deck is stacked from the beginning.

    My theory goes like this, and I have been researching this for several years. As well as having some formal education in chemistry. Links to my threads and others are attached. And of course, it’s cold again and this is on my mind. It is a problem that I have not fully solved yet. As an engineer that is unacceptable.

    The tubes of the heater core look to be a copper or brass alloy. And there are static mixer elements within the tubes that are made of the same material. These metals are both very reactive as a catalyst. The static mixer elements increase the mixing of the working fluid and decrease the width of the passage.

    Now factor in that ethylene and propylene glycol are in fact solutions of low molecular weight polymers. That will slowly react and form a higher molecular weight polymer. 98greendash wrote about a late model VW that had only ever had VW coolant in it that did the same thing. I also recently discovered some research about silicate suspensions in coolant reactions particular to dexcool and it has led me to the following conclusions:

    In a brand new, clean system the drive to polymerize is very low, the coolant properties are such that they can resist their own desire to solidify. But by default of it’s function as a corrosion inhibitor it does react with metals, and also a bit with the plastics and rubber.

    As the systems age, contaminants foul up the chemistry and almost inevitably lead to some polymerization here and there which is usually of minimal concern. You can see this coating inside the hoses and coolant passages of any engine you teardown, regardless of make. In the heater core of a VW this coating is a sticky waxy brown goo.

    Now, the more surface area you have, the more reaction you will get. And the cooling system and every one of those flakes has a lot of surface area. So when you flush, you reset the chemical reaction equation, but you never fully reset it to zero, because you never get all of the contaminants fully removed. Thus the effective life of the coolant before you start getting polymerization will always get shorter as well. Successive flushes will get you closer to zero, but never back to zero.

    Now here’s a fact all of us can agree upon – As long as the car doesn’t overheat we don’t care about all this microscopic polymer contaminant crap – so NBD.

    BUT - the part we do care about is where all this microscopic crap gets circulated through a device full of tiny passages coated with sticky goo. This microscopic crap builds up, causes more reactions, makes more goo and so on. End result is that even with sufficient coolant flow, you will still have minimal heat because the factory core was undersized to begin with, had static mixer elements to try and compensate, and then the whole mess gets coated with sticky goo that both insulated the tubes from heat transfer and reduces the effectiveness of the mixer elements within the tubes.

    My analogy for this would be the way mucous coating your lungs / sinuses removes particulates from the air you breathe.

    So long story short, even factory coolant left unattended will do this. All coolants polymerize to some extent. But our cars have the fortunate combination of this coolant reaction and a heater core that works like a coolant filter. The heater core is destined to fail from day one. And most of the solvents available to dissolve the wax will also dissolve the plastic tanks and gaskets on the ends of the core in sufficient concentration.

    I am searching for a good solvent recipe now because my wife is complaining that my fix in the 3rd thread below leads to a car that is too warm this time of year, and she runs the AC the whole time she drives, even with the shutoff valve only cracked open slightly. It also leads to interesting defrost and windshield fogging (raining) scenarios when you turn the AC off. But if cold weather would arrive quickly, this problem would be fairly minimal.

    The shorter chain (low molecular weight) PEG monoesters are in fact water soluble. The higher molecular weight chains become waxy and can only be removed with polar solvents. Xylene is the most common but would be very bad for the tanks and gasket. On the other end of the spectrum is kerosene, mineral spirits, and naptha. I suspect these three would be safe on the tank. But am still investigating. If I had a bad core I would try it on that first. Maybe I can pick one up at the VW dealer scrap bin!

    To be honest (based on past work) I suspect my half-assed work thus far would be enough to support a legal proceeding in this matter. But at $1000 a car I don’t think we could get a lawyer to take it.

    So if I can find a sufficiently reliable solvent solution to get the factory core clean I will re-connect it. But my previous 3 flushes with citric acid and CLR only yielded results measured in days. I’m looking for results measured in months – like at least 4 months!

    What your heater core looks like.

    http://www.passatworld.com/forums/42...than-once.html

    $35 & 3 hour no heat fix - guaranteed!

    Particularly this picture:
    http://www.passatworld.com/forums/42...an-once-2.html

  6. #5
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    Try This!

    About a year ago I realized I wasn't getting much heat from my heater (A4 V6 Audi). I bought some Prestone sodium citrate flush (sounds like lemonade to me) and flushed the core several times. I used a very hot flush solution, forward and backward through the core several times. Then multiple flushes with plain water. I used compressed air to blast the water out of the core. Some crud came out but not enough that it seemed like it would make a big difference in the heater performance.

    So I went back to the two-part flush widely used 30 years ago: oxalic acid flush + sodium carbonate neutralizer. I couldn't find this in an auto parts store but the chemicals are readily available. Oxalic acid is used as a wood bleach and any good local hardware store should carry it. Sodium carbonate is used in swimming pools to increase the pH. If you're just flushing your heater core you'll only need a few tablespoons of each chemical to make up a solution. I wrote up my procedure somewhere but I can't recall where right now. Basically, mix the oxalic acid with very hot water and pour it into the core using clear vinyl hoses. I alternately raised and lowered the hoses so the flush would move back and forth through the core. I repeated that a few times and then went to the neutralizer. I have read you shouldn't leave the neutralizer solution in the core for longer than 15 minutes if there's aluminum in contact with it. But from what I can tell the Audi core tubes look like copper or bronze. Anyway, I observed the 15 minute rule. Lotsa crud came out after the flush. Interestingly, the neutralizer solution was black as coal when I purged it from the core. I repeated the process another time and got more crud out. Again I used compressed air when getting both solutions out of the core. I recommend eye protection and rubber gloves. Make sure the hose ends are securely fastened in your catch bucket if you're using compressed air. It's a year later and I still get great heat. The car has 196,000 miles on it and is going on 12 year old.

    When GM had its problems with DexCool sludging (or whatever you wish to call it) they issued a technical service bulletin and recommeded using the two-part flush I mentioned to clean out affected engines. If you search for DexCool TSB I'm sure you can find it. They have a lengthy procedure to clean up the entire coolant system. I cleaned just the heater core since I had no other symptoms besides very little heat.

    If you do try this let me know what kind of results you get.

  7. #6
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    Quote Originally Posted by BikerBill View Post
    About a year ago I realized I wasn't getting much heat from my heater (A4 V6 Audi). I bought some Prestone sodium citrate flush (sounds like lemonade to me) and flushed the core several times. I used a very hot flush solution, forward and backward through the core several times. Then multiple flushes with plain water. I used compressed air to blast the water out of the core. Some crud came out but not enough that it seemed like it would make a big difference in the heater performance.

    So I went back to the two-part flush widely used 30 years ago: oxalic acid flush + sodium carbonate neutralizer. I couldn't find this in an auto parts store but the chemicals are readily available. Oxalic acid is used as a wood bleach and any good local hardware store should carry it. Sodium carbonate is used in swimming pools to increase the pH. If you're just flushing your heater core you'll only need a few tablespoons of each chemical to make up a solution. I wrote up my procedure somewhere but I can't recall where right now. Basically, mix the oxalic acid with very hot water and pour it into the core using clear vinyl hoses. I alternately raised and lowered the hoses so the flush would move back and forth through the core. I repeated that a few times and then went to the neutralizer. I have read you shouldn't leave the neutralizer solution in the core for longer than 15 minutes if there's aluminum in contact with it. But from what I can tell the Audi core tubes look like copper or bronze. Anyway, I observed the 15 minute rule. Lotsa crud came out after the flush. Interestingly, the neutralizer solution was black as coal when I purged it from the core. I repeated the process another time and got more crud out. Again I used compressed air when getting both solutions out of the core. I recommend eye protection and rubber gloves. Make sure the hose ends are securely fastened in your catch bucket if you're using compressed air. It's a year later and I still get great heat. The car has 196,000 miles on it and is going on 12 year old.

    When GM had its problems with DexCool sludging (or whatever you wish to call it) they issued a technical service bulletin and recommeded using the two-part flush I mentioned to clean out affected engines. If you search for DexCool TSB I'm sure you can find it. They have a lengthy procedure to clean up the entire coolant system. I cleaned just the heater core since I had no other symptoms besides very little heat.

    If you do try this let me know what kind of results you get.
    Used your method to flush my heater core yesterday and I'm please to say it appears to have worked. The whole thing started with coolant getting mixed with the green stuff at a oil change joint, the gel and crud showed up in the resevoir and no heat. Tried to flush the system several times after replacing the thermostat, never could get the thermostat to open. Replaced the radiator, yadda, yadda, yadda.. Found a VW mech with his own shop and along with fixing some other issues, he flushed the heater core twice using concrete cleaner. They had a guinnie pig vehicle that this had worked on, but a mile down the road, no heat, been like that for over a year. My mechanic replaced the coolant with Dexcool when he flushed the system, replaced the thermostat, the water pump and I've never notice anymore crud or gel forming in the resevoir, that's what I've been topping it off with to avoid anymore mixing. Tried flushing the core more times than I care to recall and your method finally worked. Anyway thanks, let you know if it lasts.
    Regards,
    Dave

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