What is this Dexcool reservoir sludge/gel, and how do I get rid of it?

[Oro_O]

I went to do a radiator drain/fill on a family 2007 Equinox today. I last serviced that in 2017, 43.3k miles ago, refilling it then with NAPA dexcool per my notes. Nothing added since then.

There was this nasty white gel in the upper part of the reservoir, and a serious brown sludge in the lower part. If Marla Singer were around, she’d try making soap out of that white stuff; it’s nasty.** I can’t access the whole reservoir (wall in the middle) to stick in a brush to clean it fully. I fully admit I very probably have not looked in here since 2017, but I know it did not look like this then or I would have done something. The coolant itself is fine - what drained out of the radiator was perfectly normal looking.

- Is this just from water/air getting in the reservoir and oxidizing the Dexcool?
- What will dissolve this? I have tried vinegar, Krud Kutter so far with limited success, scrubbing in the small area I can reach via the opening. Try stronger Acid or Base? I have the reservoir on the bench filled with a solution now to try to dissolve some of it overnight. The gel dissolved in vinegar but the sludge is another matter.
- 143.1k on car now, 99.8k last time I did the coolant. We have had the car since new (my parents’), so no one else has touched this other than the dealership early on.
- Again, this is ONLY in the reservoir, not in the system at all, so I’m not overly worried other than cleaning out the reservoir.
- I think I will flush it thoroughly and switch it to Peak 10x; this just seems weird.
- This is the only DexCool vehicle I regularly service so I’m no expert on DexCool; opinions welcome.

** That’s my required Chuck Palahniuk / Fight Club reference for the week.

 

[jetman]

buy a new tank
I run Dexcool in 3 of our vehicles and never see that or have a problem caused by the Dexcool.

 

[atikovi]

Dump in a half cup of bbs or steel shot along with a degreaser like Fantastik, 409, Simple Green, etc. and some hot water. Cap off the openings and shake real good. Then dump out into a strainer and rinse. Repeat as needed. I've done it on 40 year old bottles to make them like new.

 

[Chris142]

That kinda looks like atf to me

 

[Oro_O]

Dump in a half cup of bbs or steel shot along with a degreaser like Fantastik, 409, Simple Green, etc. and some hot water. Cap off the openings and shake real good. Then dump out into a strainer and rinse. Repeat as needed. I've done it on 40 year old bottles to make them like new.

BB’s - good idea. I have done similar with mortorcycle tanks in the past. I have a small milk carton of BBs in the garage. Next smallest loose projectiles I have on hand are some 77gr 224 Sierra Match Kings; don’t want to waste those on this. . I’ll try the BBs.

I added some HCl to it so it was about a 15% solution, it did nothing at all, either.

 

[Oro_O]

buy a new tank
I run Dexcool in 3 of our vehicles and never see that or have a problem caused by the Dexcool.

I’m not a Dexcool hater by any stretch; just wondering what is going on. If I were, I would have swapped it years ago. The only other person who could remotely have touched it would have been my dad. I asked him and he said he’d never touched it since the low level light never came on, plus he knows not to use anything but Dexcool.

If I can’t get it clean I’ll get a new reservoir. That sludge is weird and persistent - and somewhat oily. I wonder if there was a contaminant in the NAPA Dexcool batch I used last time - that oxidized up in the reservoir but not the system.

ETA: I tried BBs + the strong acid solution and it did very little. I dumped that out and switched to a strong base (bleach) and BBs and it was making good progress. It’s hard to get the bbs into all the baffled sections, plus it takes a lot of shaking, but it’s getting there. So thanks @atikovi as that idea is helping.

 

[Soft Cars]

Rock salt and shaky shaky.

 

[Kira]

A pal had a jug of swimming pool pump cleaner which transformed a filthy tank into new looking , snowy white plastic.
I was floored.
Alas, the label was gone so I have no clue what the stuff was.

 

[JohnnyG]

That could be from some kind of stop leak. It is sometimes added at the factory.

 

[Oro_O]

That could be from some kind of stop leak. It is sometimes added at the factory.

I have no idea what it is, but it’s a tenacious brown sludge stuck all inside the reservoir - the pic does not show it well enough or how much it is. Slightly worried it could be elsewhere in the cooling system.

Finally I got the reservoir clean with diesel fuel and ball bearings. The strong acid and base didn’t phase it much. So I switched to a non-polar solvent and that did the trick. Coolant should be non-polar because of the glycol, water, etc. Whatever this was came from elsewhere and we cannot fathom how it got in there, since we’ve had the car since new.

I will flush the system and replace with an AMAM - Ace has the Peak10x on sale now so I’ll go buy more (already got some last week for the tractor).

 

[kschachn]

Finally I got the reservoir clean with diesel fuel and ball bearings. The strong acid and base didn’t phase it much. So I switched to a non-polar solvent and that did the trick. Coolant should be non-polar because of the glycol, water, etc. Whatever this was came from elsewhere and we cannot fathom how it got in there, since we’ve had the car since new.

Glycols are polar, just like water. You'd have a hard time making a solution if they weren't.

 

[kschachn]

That kinda looks like atf to me

I would definitely check for this.

 

[John105]

buy a new tank
I run Dexcool in 3 of our vehicles and never see that or have a problem caused by the Dexcool.

Me neither. I even put Dexcool in my Nissan, mixing it with green Prestone, and ran that 7 years....I didn't know they were not compatible and it was all I had at the time...

 

[Oro_O]

Me neither. I even put Dexcool in my Nissan, mixing it with green Prestone, and ran that 7 years....I didn't know they were not compatible and it was all I had at the time...

What causes it, per GM and Texaco, as I have read is air. Not mixing, but air in the system. DexCool apparently is HIGHLY susceptible to oxidative damage, and the silicates drop out of solution and form this brown, oily sludge. The reservoir has about five separate baffled compartments to minimize air contact (it took me about 1/2 hour to get the BBs out because of that), unlike any Japanese or European coolant reservoir I have ever seen. So either the car has some residual OLD original dexcool in it that gave up the ghost, has a minor air leak somewhere, etc.

So from what I have read on a BUNCH of GM-focused forums last night, this is exactly what DexCool does when it oxidizes badly. You get that brown sludge as well as sometimes that white fatty vaseline-like stuff.

I’m going to drain the radiator and block and refill with water each day for four days (already did it today; she’s out driving it now). Then flush thoroughly again and put in Peak 10x.

 

[Rand]

driving it with water only for 4 days is sorta extreme, I'd be more worried about that causing issues.

Maybe use some prestone super flush?

 

[Oro_O]

driving it with water only for 4 days is sorta extreme, I'd be more worried about that causing issues.

Maybe use some prestone super flush?

It will cause nothing other than to clean the system; that period of time is not extreme. Then you run a citric acid flush to remove any scale and then fill. Long-standing method and I’ve done it on several vehicles over the years. Obviously you don’t do this in winter below freezing.

I don’t want to crawl underneath and dump boiling water on me from the rad hose and block tap 4x in a row. I can let it cool down and drain it cold each time this way. Also when I refill it, I use concentrate and bump it to 60% concentration. This gets in 20% more (compared to 50% concentration) corrosion inhibitors, additives as extra insurance.

Running on water long-term is of course a very bad idea. A lot of auto-crossers and similar will run water all summer during the season, do a flush to de-scale, then switch back to regular coolant in the fall. I never used to do that but some guys I knew/went to autocrosses did.

 

[Rand]

Well with the cooling fans coming on ever later (higher temps) on late model vehicles you dont have as much margin for error and could see localized boiling in the wrong conditions imo.

A vehicle equipped with a tigershark 2.4 can see coolant temps around 230f for example.

 

[Oro_O]

Well with the cooling fans coming on ever later (higher temps) on late model vehicles you dont have as much margin for error and could see localized boiling in the wrong conditions imo.

A vehicle equipped with a tigershark 2.4 can see coolant temps around 230f for example.

Boiling point of pure water in a cooling system is 250F. (2atm). Boiling point of 50/50 mix is 270F. Not much risk.

Also, pure water transfers heat out the radiator WAY better than a mix or pure glycol. So temps are actually lower w/pure water than mix. That is why racers do it.

 

[kschachn]

Heat transfer is better but the temperature is not necessarily lower. Unlike racing a street car is controlled.

 

[jetman]

I’m not a Dexcool hater by any stretch; just wondering what is going on. If I were, I would have swapped it years ago. The only other person who could remotely have touched it would have been my dad. I asked him and he said he’d never touched it since the low level light never came on, plus he knows not to use anything but Dexcool.

If I can’t get it clean I’ll get a new reservoir. That sludge is weird and persistent - and somewhat oily. I wonder if there was a contaminant in the NAPA Dexcool batch I used last time - that oxidized up in the reservoir but not the system.

ETA: I tried BBs + the strong acid solution and it did very little. I dumped that out and switched to a strong base (bleach) and BBs and it was making good progress. It’s hard to get the bbs into all the baffled sections, plus it takes a lot of shaking, but it’s getting there. So thanks @atikovi as that idea is helping.

You might try this, its very effective. It comes in lesser quantities.