Hey guys, weird situation.
In the past two month I have gotten a low coolant light on the dash. Added coolant both times to the max, bout once a month. Today I come out after driving for 1.5 hours in 88 degree weather and there is a large puddle of coolant on the driveway. I took the coolant tank off and tilted it, started pouring around the transmission area. tested with water, same thing. I mounted the tank back and attached all hoses, added water again, ran car. No leak!!! wtf?. Tilted the tank, no leak, drove car around for few minutes, no leak. What is going on?? could it have been overfiled? I have to drive 130 miles to a wedding tomorrow and don't wanna take a risk. Any ideas would be much appreciated.

 

generally the A6 leaks from the coolant tank or the after run pump(2.7), besides the obvious hoses and such. The leak might be from something metal, it's expanding when hot and leaking, then shrinking when cool and sealing.

That's all the help I can provide. Sorry.

 

If you can't see the leak, it helps to get a pressure tester and get the cold system up to 15 psi and watch, it should leak then. This is a tool that can be used over and over, a good investment if you are tempted to fix things yourself. The only bad thing is this car has a goof-ball large fill opening on the coolant tank (why do engineers do this dopey off the wall stuff to things that don't matter?), it will require adapting a connector somewhere else in the system.

 

A fairly common leak, which will appear at the bellhousing area, are the coolant pipes under the intake manifold. Coolant leaks into the engine valley and runs out the back. There's o-rings where the pipes stick into the block in front. They usually leak a little for a while then suddenly the coolant just pours out. To replace them is fairly involved. You need 5 o-rings total (and of course intake gaskets). Two for the front connections, two for the coolant manifold on back of the heads (you need to remove it to get the other tubes out) and one more where the left side tube connects to the coolant manifold. I've done these at work a few times on the 2.7L and 2.8L engines. It's about a 3 or 4 hour job. Think we charge 3.5 hrs (Audi Dealer). Yes, the aux coolant pumps can leak but most times it's more seepage than a huge gushing leak.

 

Sounds like your coolant reservoir cap has gone bad or was loose.

Bob

 

The leak you have may be behind block on the lower pipe. It probably looks a lot like this. I took the tranny out to fix mine. Took 4-weeks to remove the trans. and 10 minutes to replace all the O-rings ( about 10 bucks from Audi ) get them from the dealer, as the two that contact the block are of high-silicone content to handle the heat.

Sorry the photo will not load

 

I had the tranny worked on in early to mid April, not sure if that can have any influence on this issue but I suppose it can help me slim it down a bit.

 

Not sure if this is specific to your issue, but last year I had the same relative thing happening. When stationary, for the most part, I could not get the leak to show up, but it was no doubt dropping coolant (evident by the empty tank and pink residue all over the under carriage). Turns our mine was leaking at the "auxiliary" water pump and was only leaking enough to puddle in the skid pan so I wasn't seeing it when it was parked.

Anyway, hope that's not your problem as this was an expensive fix (cheap part, expensive labor).

 

You should look at the water pump; I had that happen on my A4 2.8 a while back. Every once in a while it would dump a quite a bit out, but would be fine when the engine cooled down. Water pump replacement can get quite expensive, might as well chage out the timing belt at the same time if you find it to be the water pump.

 

I had this problem before. Coolant leaking and then I diagnosed where it came from or how it happened. It was my coolant reservoir cap indeed that was loose enough.