Good flush products for Dexcool sludge?

My Buick with a supercharged 3800 is running hot occasionally in stop and go traffic. About six months ago, I repaired a lower intake manifold gasket after having the parts changers at the local stealership misdiagnose the problem as a radiator fault and replace the radiator. The car is using Dex-Cool, and it's taken on that nasty, brown, silty look. I'd like to flush the coolant out and put something that won't sludge up in there. What products have you found work well for removing Dex-Cool sludge?

https://grassrootsmotorsports.com/forum/grm/xj-cooling-system/89243/page1/

I've had good luck flushing dex sludge from heater cores using vinegar.  I generally flush most of the crap out and then soak the core with 100% vinegar for a few hours/over night and then flush with water some more.  I repeat until it runs fairly clean.  Then I fill the system with 50/50 vinegar and run it like that for a few weeks, flush, and then refill with 50/50 vinegar if it's still bad.  It then gets filled up with non dex and everyone is happy.

I've heard of people using CLR but I have no direct experience.

Thanks! So far, that's two testimonies for plain vinegar.

Be prepared for leaks. I had freeze plugs, the radiator and the water pump all as casualties in that war. 

tuna55 said:

Be prepared for leaks. I had freeze plugs, the radiator and the water pump all as casualties in that war. 

Thanks for the heads up. Sounds like the classic "the rust was the only thing holding back the leaks" scenario. Not sure there's anything effective that would avoid that if it's the case in my car.

Do they still sell the cooling system flush where you cut a heater line and spliced in a T fitting and hooked it to a garden hose?  Then just run the car with the radiator cap off and let everything flush until it runs clear.  Without a constant supply of fresh water it gets frustrating to flush a system completely.  My Monster Miata had rusty coolant and never got fully clear even with repeated fillings and drainings.

KyAllroad (Jeremy) said:

Do they still sell the cooling system flush where you cut a heater line and spliced in a T fitting and hooked it to a garden hose?  Then just run the car with the radiator cap off and let everything flush until it runs clear.  Without a constant supply of fresh water it gets frustrating to flush a system completely.  My Monster Miata had rusty coolant and never got fully clear even with repeated fillings and drainings.

 

This?

Yep, still around. But I thought this one might also need chemical assistance.

I wonder about flushing with water and then filling it with cheap knock-off Coca-Cola and letting it sit for a day then flushing with water again.  

Preston coolant flush worked well for my dad's s10. But at work we normally just flush with water and antifreeze until it becomes clean. Our flush system holds 5 gallons and rarely do we have to refill it before the fluid comes out clean.

My Dexcool cars just get a water flush.  The sludge that they get is a silicate precipitant, so any chemical that would successfully dissolve it will also dissolve the block, intake, and your hands.

If anything, you don't need an acid like vinegar, you would want a base like soap.  Acids tend to increase surface tension, bases reduce it.  Think of this like using soap to help physically get mud off your paint, not an acid to chemically dissolve rust on a spindle. This is a physical thing, not a chemical one.  You're scrubbing, not dissolving.  An acid would be counterproductive.  Bases would assist the water in surrounding the particles and suspending them.  Same concept when you use dish soap to lift lasagna off last night's pan.

On my LT1 (after three heater cores under warranty) I drained the block and radiator, closed it back up, pulled the heater return hose and thermostat, and backflushed for about a half hour with water.  It was like watching a sci-fi horror movie.  The sandy brown jello that poured out of that system was like watching an oozing alien corpse.  I caught the first 5 gallons in a bucket, (because environment) then let the rest drain in the driveway.  When the driveway dried it was covered with tan sandy stuff.  I refilled it with water and drove it for a few days and re-flushed.  It was pretty clean so I just refilled with Prestone generic green 50/50 and never had another problem.

But honestly.... I don't think you need anything but water.  No need to risk foaming with a base, and no need to risk acid etching with vinegar.  You also can't get all of your water out when you flush, so you risk leaving vinegar behind which could react with the organic acids in whatever coolant you choose to put in.  Straight water is always safe, and in this case, I think 99% as effective.

If I ever buy another dexcool vehicle, it will get flushed and refilled with a better coolant the first day off the lot.  There is a reason GM has filed multiple lawsuits with Havoline over this debacle.

That's a bit surprising - I didn't expect the sludge I saw in there to be a silicate. I'd cleaned a fair amount out when I'd pulled the intake manifold. The stuff in there was oily and gooey, almost like Vaseline.

I never found the vaseline stuff in any of mine.

The main things I found over my few DexCool cars were that it is more like half-set jello.  It does feel greasy unlike jello, but it was never that vaseline consistency.  I have found vaseline in water jackets where there was a previous head gasket failure.  Seems like any oil that got into the coolant gets gelatinous over the years and hangs out in the nooks and crannies.

I put an intake manifold on a 454 and put a little smear of silicone around the water passage in the gasket.  Before I knew about the evils of Dexcool, I decided to use some because a friend gave it to me.  A month later I had to pull the manifold because the machined pad where the distributor sits had been machined to far causing an oil leak and Edelbrock had sent me a new one.

The black silicone I used around the water passages had seeded a growth of stuff that looked like orange rock candy.  When I pulled it off, it was slimy like Flarp (that slime stuff kids play with) but also had super fine grit in it and the rock candy structure was more like Knox Blox (those jello finger foods where you add double the gelatine).  In just one month it had closed off that passage by probably 1/4 of the cross section.

That's when I started researching DexCool.

The verdict is kinda questionable on the Vortec engines, but they used a silicone imprinted intake manifold gasket, and the assumption was that their frequent intake manifold coolant leaks were due to that same seeding from DexCool.

Most coolants have silicates in them as silicon compounds (not to be confused with the above mentioned silicone... a whole different animal).  They are suspended in solution and usually don't cause any trouble, but the OAT (organic acid technology) used in Dexcool does not use silicates and is far less stable at holding the silicates in solution.  Since your engine is made with a sand casting, its full of silicon.  If they precipitate out, again, no worries.  The silicates themselves aren't the problem.  The larger issue is that those silicates are then reactive once they drop out.  In GM's case, they almost always use clay tablets (with silicates in it) in their cooling system.  Its an old-school trick.  If a small leak develops, the clay plugs the hole.  Its one penny of prevention that might prevent GM from paying warranty repairs.  The clay in the tablets doesn't play well with the OATs in the Dexcool.  The downside is that no amount of flushing will truly ever get all the clay out of the pores of the block.

Dexcool itself isn't necessarily evil, but its fragile.  If you have a brand new block and use distilled water, you might get lucky, but expect trouble.  Dexcool is remarkably good at corrosion protection.  The Silicates (a combination of silicon, oxygen, and one of a bunch of possible metals like boron, potassium, manganese, aluminum, and sodium) are more electrolytic and can cause more corrosion.  No silicates = less bimetal corrosion.

Now that I think about it, the Vaseline-like consistency may have been the sludge after I'd sprayed it with brake cleaner. There definitely seemed to be more than silicates to the sludge.

What years is this evil dex-cool crap?  I've heard horrific stories but never any years of use in GM products.  Please tell me not 2005's.....please.

I found this thread on Google, just an hour and a half after you started it.

You guys rock.

44Dwarf said:

What years is this evil dex-cool crap?  I've heard horrific stories but never any years of use in GM products.  Please tell me not 2005's.....please.

Started in 95.  Was still in use until at least 08 but I lost track.  GM signed a stoopid long contract with Havoline and they've been suing them ever since.

Just flush and fill with something better.  It is great at corrosion resistance, so if you haven't had sludge issues, now is the time to flush it out and send it to hell where it belongs.

Late-model confusion can happen with compatibility.  Some of the OAT concoctions use 2-EHA (ethylhexanoic acid) which is a plasticizer and degrade plastic parts in the system.  For the most part, I just go back to the old silicate green stuff and change it more frequently. (silicates break down faster than OATs)

A fantastic writeup on the topic HERE

Update: Drove it for 100 miles with a gallon and a half of white vinegar in the system. The I did a flush with the Prestone garden hose setup. Got a lot of crud out of the radiator, but engine temperatures are unchanged. Looks like I solved a problem, but not the problem.

There could still be some air in the system. One way to do it was to remove the thermostat housing and fill the system, then replace the housing and use the air bleed screw to get the rest out. This worked on the Bonneville I had with the regular 3800. Also, did the thermostat get changed? If it is older, might be worth replacing. Just a couple thoughts.

Thermostat was replaced earlier this year.

There appears to be a few bubbles working their way out. I had used the official GM procedure for using the air bleed screw, but that really, really doesn't work.

I have had pretty good luck using automatic dishwasher detergent in the system.  From what I've read, it's kindof like a poor-man's water-wetter.  Like Curtis said, you want to reduce the surface tension to flush the carp out.  Automatic dishwasher detergent doesn't suds (the new HE clothes washer detergent would probably work, too) so it cleans without creating a nasty mess of bubbles.  

Add maybe a cup or so of the soap to a radiator about half-full of just water, then fill the rest of the way with water, run it for a while (not when it can freeze!), flush, backflush, and repeat as needed.  

Also, take the thermostat out when you're flushing/ backflushing.  That'll help keep things moving through there.  May want to remove the radiator, too, and flush clean water and let it just eject onto the ground.  The rad could be full of garbage- the one on Mrs. VCH's Suburban (and her Jimmy before that) were heavy with crud.  

A good shop can flush a rad for about $60.  

tuna55 said:

Be prepared for leaks. I had freeze plugs, the radiator and the water pump all as casualties in that war. 

On a 3.8 of that vintage, the water pump is a 40k maintenance item anyway.

I was told somewhere to use dishwasher detergent.  Not dishwashING detergent, but the stuff you put in a dishwasher.  Cascade, I think.  Worked wonders on a hard to find RX-7 radiator that was full of sat-for-10-years gunk, and apparently it is called out in GM service bulletins for cleaning out cooling systems after an oil in coolant episode.

I'd just drive it.  The oil will filter to the overflow tank, which can be replaced after a couple months.  If itmis genuine sludge and not just oil in the system, replace the radiator and heater core.

MadScientistMatt said:

That's a bit surprising - I didn't expect the sludge I saw in there to be a silicate. I'd cleaned a fair amount out when I'd pulled the intake manifold. The stuff in there was oily and gooey, almost like Vaseline.

Then it was probably oil.  Leaking gaskets leak both ways, on cooldown the cooling system will suck oil in from the valley.  Dexcool Sludge is more like a dark red clay.