The car is a 2001 A6 2.7T with 116,000 miles on it. I was traveling for work last week and, after a 520 mile drive out to Middle-of-nowhere, NY, I noticed a puddle under the front of the car after it had sat in the hotel lot over night. A swipe with my finger confused me: it was pink (ah, G12!), but oily (uh, Mobil 1?) (I have since learned that the water evaporates quickly from G12, leaving an oily residue) Anyway, at the time, I popped the hood and noticed the reservoir was low... a about 10mm below the "MIN" line. Since I was 520 miles from my tools and dirty clothes, I had to let it go. I got back home yesterday (after another 520 miles without incident, thankfully -- but during which time I had plenty of free moments to consider what it would be). I was betting on the auxiliary coolant pump.

Popped the plastic covers today and spent the next 20 minutes puzzled that I couldn't find any indication at all of coolant residue on top of the block under the manifold. I guess it isn't the ACP. After some searching here, some other common leaks were suggested to be the overflow tank itself (seems clean to me), the oil cooler behind the oil filter (dry as a bone), and the water pump (I hope it isn't this! -- the TB/pump were replaced at 70K miles, so about 45K ago... coming up on another replacement, but still have time, I think).

When I was under the car at the hotel, I noticed a fresh drop of coolant hanging from one of the bolts on the oil pan on the passenger side. Looking more closely in that area now, I find LOTS of sludgy oil on the passenger side of the block behind the alternator. No coolant residue, though. I have seen posts suggesting the upper sump gasket is in this area -- along with some turbo oil lines with o-rings -- but I'm dealing with a coolant leak, not oil. Perhaps there are two things wrong, here. But, one at time.

Where else should I be looking for a coolant leak? During my trip to NY, I only saw puddles twice - once just after my trip out... and once about three days later. So, it doesn't seem to be a persistent leak. In fact, there wasn't a puddle since parking after arriving from the 520 mile return trip -- though I expected to see one. What is the best indicator of a leaking water pump?

Thanks in advance for your opinions...

JWeb