This thread serves as a catch-all for coolant system issues on the C6 S6. Feel free to add any info or questions of your own, and I will keep this first post updated as we continue to learn more.
As these cars are starting to gain some mileage, we’re learning that many coolant components are starting to fail around 80k-120k miles. With so many parts to fail, and each one taking your car out of commission until it gets fixed, it may be wise to address as many of these items as you can, as a preventative measure, after your car exceeds 80k miles or so.
Symptom: Coolant leaking behind the passenger wheelwell
http://i.imgur.com/BIoDAFA.jpg
Cause: Most often, this is caused by either a hairline crack in the expansion tank, or a bad gasket in the expansion tank cap. A bad cap will cause coolant to leak out the overflow hole in the bottom of the tank (pictured above).
Solution: The cap is a $5 part from Amazon or any auto parts store. The expansion tank I believe is about $80 or so. Both can be replaced relatively easily yourself.
Symptom: Coolant gushing out the end of small hose(s) behind the expansion tank
http://i.imgur.com/rubC6qD.jpg?1
Cause: The Y connector on the small overflow hoses going into the expansion tank broke.
Solution: As far as I know, you cannot buy the Audi Y connector by itself, it comes in a kit with new hoses attached to it, and costs around $150. If your hoses are still in good shape, you can replace the plastic Y with a $5 brass T fitting from your local hardware store.
Symptom: Coolant is dripping or gushing from here:
http://i.imgur.com/L1xWuZo.jpg
Cause: The main radiator has formed a leak. This seems to happen after repairing other coolant leaks - when the coolant system returns to normal pressure, it can cause an aging radiator to rupture.
Solution: New radiators cost about $350 online, or $550 from Audi. Labor for this at a shop should be about 3.5 hours.
Symptom: Coolant is leaking on your exhaust, creating lots of smoke/steam:
Cause: I’m not exactly sure. A coolant hose leak somewhere. Need to look into this more.
Solution: My local shop charged me $500 to replace the coolant hose in question, but I don’t know what hose it was, nor how much the part by itself was.
Symptom: Coolant is leaking behind radiator:
Cause: If it isn’t the radiator itself, it could be the water pump or radiator hose.
Solution: A new water pump is about $400 and I believe 1-2 hours of labor. That’s also a good time to address the accessory belt and belt tensioner if those are showing age. Radiator hose is about $80.