Today, about a 1/3 of the way into my 70 mile trip my car starts to overheat. I pulled off the road and let it cool down and check under the hood to see what's going on. Lots of things were wet but couldn't see where it was coming from. Drove up the road a mile and got some antifreeze and topped it off. Drove a few more miles and it starts to heat up again (all the while the heater is working fine). I pull off the off ramp and let it idle a bit... stops heating up but doesn't get cooler either. Drove a few more miles and then stopped at an Audi mechanic I knew was along the way. After a short description of what's happening he make an educated guess and says the radiator is clogged. Sure enough that's what it was. It un-clogged itself shortly there afer and I drove the rest of my trip with no more problems.

So I'm going to replace the Radiator, anyone have any suggestions of which brand and where to buy?
Also, I'd like to clean out the coolant system before replacing the radiator, is there a chemical that can be added to clean things out or do I just have a system flush done at a radiator shop?

 

I got my radiator from German Parts Online. In stock, fast shipping, best price I found for mine. I would completely flush your coolant and put in new G12 coolant. I would also definitely replace your T-stat while in there, and maybe even consider doing your timing belt/tesioner/ and waterpump if you have a 1.8T. Flush it out yourself with a garden hose.