I have a bit of a problem. A year and a half ago, when I first bought my car, I changed the thermostat. When doing so, the car had dexcool that I was looking at going ahead and changing to green. I flushed the radiator out until just clear water came out (not thinking about turning the heater on to get it out of the heater core) and forst winter comes around and I run the heater, gunk from the mixture forms. I have been scraping it from my radiator filler neck, then running water till clear comes out ( it is almost all brown) and run the car with heater going and garden hose in radiator for 30 mins after radiator has clear water coming out. I have had the radiator professionally flushed three times, and its still doing it. I used to have to do this (ghetto flush) once a week, this time it has been 4 months. Is there anything else I can do?

 

Are you sure its still gunk from mixing the too? Gunk can form in the radiator when oil mixes in as well. Does your antifreeze have a oily rainbow effect floating on top in the reservoir?

Sometimes getting the antifreeze gunk out can be a pain. I rain straight water in my car for a couple weeks, making sure not to drive too far and let it boil over. I dont really recommend that but it worked well for me. Cleaned all the gunk out that was stuck inside the block and heater core.

 

I looked up this information and nothing about any kind of "gunk" was mentioned.

http://www.cartalk.com/content/colum...August/08.html

I believe that the gunk may be from another, yet undiagnosed, problem. Good luck!

 

I have seen this horror that is Dexcool gunk in person.
It basically hardens into a super thick sludge, almost into a paste that sticks to just about anything.
Not saying that the OP's problem is definitely dexcool gunk that's just held over in some recesses in the coolant system, but it could be. I'd definitely check for oil/coolant mixing, and if you can rule that out, then check out the bobistheoilguy forums. I believe there are some threads over there about cleaning that gunk out of your coolant system. It's been a while since I've looked though.

 

Here's the way I understand it.

The sludge is a very common problem with these cars, but the cause can be several.

1.) Sludge build up in the coolant system is one thing, however if you also find it happening in your oil it means the coolant and oil are mixing at some point, this is very bad and points to a possible upper intake failure (Could be the Gasket, or even worse could be the lower intake) if this is the case bring it to be fixed immediately , could be pricey to be fixed but more so if nothing is done.

2.) However if the oil looks clean and there is a build up only in the Coolant system some point out that GM knew of leaks in the system prior to seling cars, and so the "fix" was for them to put in stop leak tablets in the system, which eventually causes the sludge, also becomes more apparent when coolant runs low.

I had the later issue for a while years after I brought my car I always had the sludge at the neck, when I did my first flush, it was crazy bad, much of my resevoir had the sludge. I think I did 2 or 3 flushes in 2 years and still had some every now and again.

This past summer I had some coolant issues and as I went through the system I was happy not to see any sludge.But still check frequently to be certain.

Unfortunately mixing the dexcool/ green stuff even a lil isn't good thing, and as long as there is no sludge or issues with the oil, the only thing I can say is keep an eye on it and keep doing the flushes as the sludge builds up,

Joe

 

Oil is always perfect. The sludge is def in the antifreeze alone.

Today, I ran water through it, the ran straight antifreeze into the rad. Two ful jugs and still some brown antifreeze came out... but not as much as usual. Took the car on a drive and no problems since... will keep posted.