cheesypoof

I have a 2001 A4 1.8T that I have owned since 2003. About 2 years ago I noticed that the coolant was a lovely brown color and there was a ton of sludge in the coolan reservoir. I figured that someone at a quick oil change shop had topped the coolant off with the green stuff and the sludge was from mixing coolant types. I never flushed the coolant in the 9 years I had the car (which I regret not doing more often)

As soon as I noticed the brown sludge, I had the coolant system flushed and refilled with G12. When I got the car back there was no heat. I flushed the heater core and a bunch of brown flakes that look like rust came out. This was the first time I ever had problems with the heat. The heat was fixed, but about 6 months later I had no heat and had to flush the system again. The interval between heater core flushes is getting shorter and now I have to do it about every 2-3 months. I have flushed it about 6 times in the last 2 years.

Everytime I flush the core I get enough brown flakes (rust?) to cover the bottom of a 5 gallon bucket.

Is the heater core getting plugged a symptom or the cause? Is the brown stuff coming from the insides of the core breaking down, or is something else in the system rusting and the rust is plugging up the core?

Would replacing the heater core (big job) fix anything, or would it still get plugged up again? How do I fix the problem permanently? I love the car and want to keep it for a few more years, but the no heat thing is starting to get old.

Would flushing the whole system again help?

I do not have any coolant leaks. No coolant in my oil.

Prospeeder

You need to replace it. I just replaced one, and pulled it apart and the tubes have a spiral "noodle" looking thing to slow water down, but they pack full of debris and can not be flushed out completely, its just not possible the core is a bunch of tubes from one end to the other, when you flush it its just flowing through the few tubes not completely blocked up, and new debris in the system just piles right back up behind them in short order. You need to flush the system very very well, and replace the core. And yes its a VERY involved job to remove the entire dashboard and heater box assembly. Expect 10+ hours

clancy

Another quyote from Prospeeder from a different thread:
The one A4 i just did a week or 2 ago, i flushed it and flushed it, and it seemed to flow great. but still just barley warm, weak weak heat.New core, hot as can be, and i pulled the core apart and found it full of rock hard debris packed in the "noodles". And this was a car that had only G12, only 90k miles, always serviced, tbelt and wp done at 80k and system flushed with fresh Audi/VW brand G12. If the thermostats warming the engine up to temp and the climate system has no faults the cores bad.

So, is there a permanent solution to this? That is other than replacing the heater core every few years?

Prospeeder

Hmm well they do make inline coolant filters

http://www.ebay.com/itm/Inline-Heater-Hose-Coolant-Filter-Inspection-System-/130598196248?item=130598196248&pt=Motors_Car_Truck_Parts_Accessories&hash=item1e68425418&vxp=mtr&nma=true&si=sTfmQj1iFX0tyT6%252FO0X9a8MuCI0%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
this ad is expired but im sure there out there.

1999Audi

Did it couple years back = its not fun...
<img src='http://img11.imageshack.us/img11/729/cqso.jpg' border='0'/></a>