Leftovers from previous coolant changes.

 

I thoroughly flushed it previously though.

 

The design of the heater core is not conducive to complete flushing. Most of the crud may come our, but some may stay. Try injecting compressed air at under 25PSIG to the water to act as a scrubber to get even more out. There are some posts around that talk about doing just that with a bought or home made device.

 

Try cleaning it like this

 

He cleaned is heater core in the car. It would be difficult to rod a heater core.

 

For some reason I kept reading "radiator" instead of heater core...no more crack for me today!

 

Someone (previous owner, car repair shop, Jiffy lube, who knows?) added non-G12 coolant to your tank without your knowledge. Supposedly G12 doesn't mix well with other blends.

 

Opt for the more oily version next go around. Less likely to get stuck in the corners, and the excess oil keeps it a little looser.

Anyway, that's a hell of a lot of "peanut butter" to be in the heater core. I think you either:

A. Need to replace the heater core
B. Buy a blast vac: http://www.google.com/url?sa=t&rct=...NGRj6cRNguYxtDPV7IYOhNpQjk4kA&sig2=PtH3hdQPnHtpnrKad_apSQ&bvm=bv.54934254,d.dmg and try this method
C. Flush it the regular way until nothing comes out of it.

That's pretty nasty. Lesson learned either way: Folks, use G12 coolant! There is a reason why VW created a specific coolant for their vehicles.

 

Looks like someone mistook your coolant tank for a porta potty... Thought the chunky chocolate milk that came out of mine was bad.

Keep flushing a lot of water through it, looks like you're already using CLR too. Could try one of those prestone flush chemicals and water for a day or two, then make sure to flush all of that out. CLR is likely stronger though.

First time I did a coolant flush on my car the brown came back within a few months, the next time, I made sure the water was spotless and perfectly clear when I was done. I drained it into a white bucket to be sure. I think I must have done it at least 25 times over 3 days, and it's been nice and pink for almost 2 years now. Neighbors probably hated me getting the car to operating temp at midnight. lol Probably would have been easier and faster if the thermostat was more accessible on the V6...

 

Looks like red heroin haha...

I've seen that in my previous vehicles from lack of maintenance - but since you've flushed before I would suggest just leftovers due to poor design..

 

 

I am sure the previous owner mixed up the coolants. I flushed it once. This is the second time I flushed it. Backflush and CLR.
Now, it works like a furnace.

 

When I flushed mine earlier in the year, I bought one of the drill pumps at Home Depot, filled the entire flush hose system with straight CLR, and the let the drill pump run for about 45 minutes the first time, drained everything and ran it again for 30 minutes the second time. This was in February of this year. Just to make sure everything worked right I flushed it again the last weekend in September, and I still got a small bit of crud out of it, nothing like you got though.
I think what you got was just leftovers from the first flush, much like mine.

 

What I did was I backflushed it. I read that it would dissolve more. So did it. I was surprised to see how all those stuff could be in the core. I used CLR but diluted it fearing that using it direclty would damage the tubes.