Jaxon

Has anyone seen this on their C6? My 06 has about 12,500 miles on it and today when I opened the cap there was a brown gunk on the inside of the cap. When I searched the forum I saw this problem may occur when you mix collants but I've owned the car since it was new and it still has the factory coolant in it. Any ideas?

CQRT

Not to sound the panic alarm . . but is the coolant cloudy and discolored too? Brown sludge is sometimes a sign that oil has gotten into the coolant . . .often from a bad head gasket or other internal engine issue where oil pressure is greater than coolant pressure - - -

If the coolant isn't discolored and cloudy-- no worries - - but if it is, get the car to the dealership pronto - - -

c6 batmobile

I agree with the above. Like you said as well It could be from mixed coolant sometimes when you take them in if the person servicing them does not know what they are doing they could mix them up.

Victoryred 08

There has been talk of a problem with Dex-cool anti-freeze turning to sludge. I had no trouble with my C5. I changed after the 5 year period as per the manual. I heard the problem was with their 4.3 c.i. motor. This was per my dealer when I asked about any trouble with it before I had my fluid changed. Hopefully, someone will have more info for you. Good luck.

WHT

The DexCool sludge looks like this. It supposedly can occur if there is a leak in your cooling system.





Hopefully, you don't have a problem.

Silver05GTO

Saw it on my LS2 GTO, brown sludge in the coolant overflow tank. VERY commonly reported. I also read on the Charger forums the SRT-8's also have brown sludge forming in their coolant overflow tanks.

Allegedly it's a know thing, and happening alot.

On the other hand I haven't noticed it on the vette, but I've had the coolant changed out a couple times within 10K miles for t-stat swaps.

LMB 4 ME

DAT B NASTY !

User 020720

foremaw

Google "dexcool sludge" and you'll see this very issue has been a hot topic for years on GM vehicles, including a host of lawsuits. There was a TSB on it several years ago, I'm not sure what the current status is. IMHO, it might be worth having someone look at it and see if it needs a flush or some other procedure before it affects any gaskets. A good reminder to all of us to keep an eye on this.

StrayDog

Made this observation ( brown goo ) on my wifes 2003 Grand Am ......when removed radiater cap , engine runs fine & no problems, but since its five years will flush / clean completely & replace with Prestone & change every two year therafter................

Just two cents from the Dog

AutoCutter

Well if it doesn't look like someone dumped a milkshake in to your overfill, then you have the famous Dex-Coolant sludge. It doesn't seem to hurt anything and doesn't seem to have any comprise of cooling-just looks really nasty. You can change the fluid, but it will be back in 10-12k

Xlr8yourC5

Take a flashlight and shine on the side/end of the tank and see if you see any film buildup on the tank sides - and I'd check the vent lines from the heads also (they feed into the top return line of the tank)
- I bought a 2005 with only 6.8K miles on it (not driven for about 9months or so by prev. owner) and later noticed sludge on the side of the tank (noticed it was a bit low one day an after opening the cap could wipe off some Dexcool mud from the tank sides...) I checked the vent lines from the head (they "T" to the return top line) and found a bit of "mud" (dexcool sludge) in them also (using a q-tip).

I had the system flushed and pressure tested - OK they said (held pressure for 30min IIRC they said) - I tried renting a pressure tested from autozone but it didn't seal well (at blow-off tube port). After seeing the "mud" in the head vent lines I was sure it was a head gasket leak (but maybe just sitting for months the air in the lines caused the mud - if their pressure test really was OK - and they just didn't pass the buck until the warranty expired (which it did in Feb...) Never saw any paste under the oil cap, none in the oil (had changed it twice previously) nor any white smoke from the exhaust (odd exhaust smell once but I think that was just from the Bassani exh. swap -no longer notice that)
Never did an oil sample test however (to check for coolant in the oil)

I was worried it was a head gasket leak but after googling on dexcool sludge was shocked at all the reports on this in the past (some horrible). Even air exposure apparently can cause this with dex-cool...

I thought considering the car was still under warranty at the time (and GM's 5yr dexcool statement) but the dealer balked - but I was glad to pay for it to get it out of there. The dealer (stealership) wrote up on the invoice that the car had been sitting for a year (which I did not say - I said 6-9 month's was my guesstimate...) - slim pickings here on dealers with any vette knowledge so I went with the closest one that had a "vette" mechanic..

Been about 5mos (but only about 1500 miles - working 6 days a week) and tank still looks ok (flashlight test) and level still looks good (filled above the full line - apparently recommended...)

I replaced the tank and cap (rather than try to clean it all out) - I was shocked to see what the original tank looked like
when I got it back (looked much worse than I thought inside... really visible once it was empty)

Just a FYI...

JmpnJckFlsh

Yep...sounds like the Dexcool scourge to me.

But...the fact that you removed your radiator cap to look in may be a clue to your problem.

Dexcool problems were discovered to be related to the system "breathing" fresh air into the radiator during cooling cycles, or from constant "checking" of coolant level by removal of the radiator cap. The fact that GM has continued to use Dexcool in spite of clear liabilities says that they believe the problems can be addressed by good design and that the benefits outweigh the disadvantages.

DO NOT REMOVE RADIATOR CAP and peer in...the reason GM put a clear overflow tank is so the coolant level could be checked without allowing free flow of fresh air into the cooling system.

In your place, I would immediately flush the cooling system thoroughly with clean fresh water. Once it was CLEAN, I would refill with Zerex G-05 or another name brand HOAT coolant formula diluted with distilled water. As indicated above, your maintenance interval after that is two years. Get that Dexcool out of there; it's toast.

Xlr8yourC5

Agreed... which is why I don't remove the cap (just use the flashlight test for sludge) - I hope it was just air exposure over that idle time that did mine.

iw172

sheeeesh, I know what I'm changin the next decent day we get here. And the wifes Trailblazer as well.

marteeni

I've also read that Dexcool becomes acidic and eats away at the gaskets, thus causing leaks. My father-in-law had 2 GM vehicles, both about the same miles, that had antifreeze in the oil. It cost him about $1000 each to replace gaskets (either head or intake, I don't recall). That's when he started researching the issues with Dexcool and joined in the class action suit against GM. I thought GM stopped using DexCool but my new 2007 convertible has it. Not sure if I should have it drained now, flushed, and refilled with Prestone (car has 1200 miles on it)? I realize 2007 Vettes have a 5-year powertrain warranty which should cover such problems, but it would be my luck that the leak would start 6 months after the warranty expired . Thoughts??

cthusker

I have an 06 and added 2 bottles of Red Line WaterWetter over a year ago. I checked my antifreeze and it's looks as good as the day I got the car. Wonder if there is something in the Water-Wetter that is preventing any sludge build-up? Getting ready for spring and the antifreeze looks good to go. It also dropped my operating temp about 12 degs on average. Perhaps I got an untended benefit from using this product

JmpnJckFlsh

I wouldn't panic just yet.

I asked about Dexcool here in 2005 before I ordered my 2006, and the general response was that no one was having a problem with Dexcool in their Corvettes. This is the first thread that I'm aware of here regarding Dexcool problems in a Corvette. I'm keeping an eye on mine, and at the first sign of deterioation, the Dexcool will be out of there.

I did have a problem in a non-GM car that was not designed for Dexcool...Dexcool WILL eat the usual elastomers used to seal cooling systems. This Toyota was constantly overheating from coolant loss until I changed back to Toyota's HOAT formula coolant.

AORoads

In addition to which, I've read that a low coolant situation just once can begin the process of producing the sludge. That and not properly maintaining the cooling system, as in changing on a regular basis. There appears to nothing inherently wrong with Dex, just a problem with maintenance and how it's used by owners and techs.

Michrider

There is nothing wrong with removing a radiator cap to check the coolant. It's not like brake fluid that absorbs water fast from the atmoshphere if the system is opened. Most overflow bottles are vented to the atmosphere anyway, those are on systems with the cap on the radiator. Surge tanks are generally sealed, but it won't trigger some grand problem if opened on occasion. Brake or other hydraulic systems should definately be kept shut as much as possible.

Those pictures of the cruddy cap and radiator look to me like something run low on coolant. Which is really a lack of maintenance (opening the radiator and checking if it's full) more than any defect in the composition of Dex-cool. If kept full it wouldn't have looked like that.

One of the biggest differences in dexcool vs the green stuff is in dexcool, everything floats. In the green stuff, all the crap sinks. So, in years past all that crap sank and you never saw it unless you took the freeze pugs out and viola there would be a nice pile of brown rusty crap. In Dexcool, it's all right there at the top of the system looking you in the face. And if left low, all that rust gets on the bottom of the rad cap and starts rusting the bottom of the rad cap in that nice little air gap caused by never opening it and making sure it is full.

S and T trucks/Blazers were a great example. I have friends that never checked their radiators in those Blazers and Jimmys, after about 3 or 4 years, gunk city under the cap and they all start raving about what crap dexcool is. My girlfriend has had a Blazer for many years that I always kept the radiator full to the top, today 6 years later that radiator, cap and overflow tank still look nice and clean. It's all a matter of maintenance.

In an 06 Vette, if there is a little brown gunk under the cap, just wipe it clean. I'd check the protection level of the coolant with one of those
hydrometers and make sure it's freeze point is around 20 or 30 below.
If the coolant checks good, there is no reason to change it.

Sometimes factory cooling system sealant also floats to the top and looks like a little gunk under the cap. If it wipes off easy, I wouldn't sweat it. If the cap looks rusty like those pics, then maybe a new cap and a coolant flush is in order. I'll bet it's just a little gunk that wipes right off, that's nothing to worry about.