Mystery coolant leak

A6 All/ S6 All
#5

I did a carbon clean on C6 S6 recently and I broke that Y shaped coolant fitting. Those plastic fittings don’t need much movement before they break because the plastic has been heat cycled so many times that they become really brittle. Instead of using another plastic fitting I went to Home Depot and got a 3/8" brass plumbing Sharkbite T fitting because that will never break like the plastic ones will.

There isn’t much coolant related by the passenger wheel well other than the coolant tank that is mounted up high. I can’t remember if the alternator is water cooled or not but I would have to assume that it is because of how hot these V10s run. The heater core is inside the car and the lines for that connect on the back of the engine. If you had a leak on the driver’s side front of the engine then that would be more difficult to pin point because there are so many lines, gaskets, and other places for a coolant leak around the water pump, thermostat, etc.

#6

Interesting… well let’s hope it was just those hoses then. I ordered the whole Audi replacement which comes with the connector and all the attached hoses for like $130, so we’ll see. I did remove the reservoir and inspected it, looked at the hoses underneath it etc, it all looked fine.

Thanks for the input, that helped alleviate some of my concern a bit. I’ll update next week once I figure it out.

#7

http://audirevolution.net/addons/albums/images/354041629.jpg

That is a trouble area at the Y. If its a lower leak you will be able to tell because you will never be able to keep coolant in the system and the coolant tank will constantly be drained.

There is a coolant line that runs through the alternator and a line that goes through the oil cooler but again if those lines are leaking the system will drain from the tank constantly.

On tie top of the passenger side there is a crossover neck on the top of the rad hose located in the front of the car just under the headlight right by the valve cover. It might be hard to see with the air box in. Those are the likely spots where coolant can come from over there

#8

I’ll give it a look, thanks for the tips. I just replaced the Y with a brass T connector from Home Depot, and that part is definitely sealed just fine now, but I’m still getting coolant dumping out when the water pump turns on. The whole tank drains dry after about 30 minutes of running the motor. I’m going to lift my car tonight and pull the wheel off and the fender liner to get a better look, I’ll report back

#9

Ok guys, I found where the coolant is pouring out from, which is in fact the bottom of the reservoir. But the weird thing is it doesn’t leak AT ALL, not even a drip, until the coolant starts to cycle. At that point, it pours out this little hole in the bottom. Is the problem the hole itself, or is this the sign of another problem somewhere else? See this video I just shot:

http://tinypic.com/r/2gv8sbn/9

#10

Here’s a screengrab from the video in case you don’t feel like watching. Can I just epoxy the hole for now, while I wait for a replacement reservoir to arrive?

http://i.imgur.com/BIoDAFA.jpg

#11

Ok, I’m pretty sure I found the problem, and once again I don’t know whether to be happy or pissed. It seems to be the reservoir CAP. The hole through which all the coolant is coming out, is this:

I’m shining a flashlight under the tank so you can see the light coming through

http://i.imgur.com/mabCpM9.jpg?1

And here’s what my cap looks like - it’s definitely falling apart:

http://i.imgur.com/zTgwsIx.jpg?1

http://i.imgur.com/vugl1yU.jpg?1

So, I did a search and found the cap on Amazon (here: https://www.amazon.com/URO-Parts-8E0-121-321/dp/B00BQS9722), and the VERY first review on it says this:

[quote]Works on my 2007 Audi S6!!!
I had a massive coolant leak on my Audi. Thought the issue was the expansion tank. However it turned out be just the cap. The stealership wanted like 30 bucks for this cap. It’s been over a week and no more issues with coolant leaks! So cheap I bought an extra one! Thanks again!!!
[/quote]
I feel like punching someone that it was so simple, and that I ripped apart so much of my car to find it. Going to try to get a new cap tomorrow, and hopefully this solves it, but I’m 99% sure it will.

#12

My local O’Reilly auto parts store was open til 10pm tonight, so I swung by and grabbed a new cap. Luckily a lot of cars use the same cap. Refilled the tank, replaced the cap, and the problem seems to be fixed. Wow, seriously frustrating how much work it took to track down the problem.

The cap has a gasket in it to prevent overflow. If the gasket fails (which mine did), the coolant leaks through that hole in the top of the expansion tank, then out through the bottom. That’s why it was so hard to find, the airbox was hiding it, and the cap itself was dry as a bone. Since another person on Amazon had the same issue with their 2007 S6, I’m highly recommending that people replace this $10 cap as part of their preventative maintenance. Just like the Y hose connector, the plastic was completely rotten and crumbling from years of boiling coolant. Thanks for the help everyone, and hopefully this will help others in the future!

#13

Great find and recommendation!

Such a great forum and group of people we have from diagnosis, troubleshooting, to resolution and recommendations to Thera :slight_smile:

#14

Scott thats impressive work. Thats not your typical issue. The Y issue happens to most cars but the cap thats just plain hard to find. I dont think I have seen that before. The cap going bad like that is just crazy. The coolant system builds up pressure over time to help move the coolant around it looks like when the pressure built up it just pushed right past the cap.

WOW again nice find. I know you said you were mad because it was so simple. Sure it was simple once you found it but even I wouldnt have thought to tell you to check the cap. Good for you

#15

What really threw me off was that it happened at EXACTLY the moment that my car got high-centered on a snow pile. Literally I was unhooking the winch hook from my car when I saw the coolant pouring out. Who wouldn’t attribute it to that? Turns out the timing was just an absolute cooincidence.

#16

im going to go check mine right no as i had to top the coolant up last week as it was below the min, no other visible leaks

#17

Check the cap and check the Y section. That can be another spot for a leak

#18

So bumping this up, I got ym car over a year ago with 85k on it. The 2nd day I had it I needed to add coolant about 1/4 of the bottle with water. Fast forward to yesterday, i’m now at 105k and my coolant light comes on. I’m down about 1/4 of the bottle again.
I’m going to order the cap, and replace the Y just as a precaution. I can’t for the life of me figure out where the coolant is going and it seems to be at a very slow rate.

I am going to do a complete coolant flush but how many new bottles of coolant do I need to refill it after I’ve flushed it with clean water?
While I’m doing the flush are there any other things that I should just replace while I’m at it? thermostat, Water pump etc?

#19

1 quart or so of coolant disappearing in 20k miles is definitely slow, almost too slow to be a leak I think. I’ve had so many different coolant leak issues on my car since I got it that I can’t honestly say what rate of coolant loss would be considered “normal” for these cars, if any. I do recall, though, that I had to add coolant to the reservoir at least once before the first major coolant leak presented itself. Seems like I’ve been chasing coolant leaks more than pretty much any other problem on this car - hopefully mine are resolved now, and hopefully your either gets resolved, or isn’t really a problem in the first place.

#20

I’m hoping that it is nothing too and I might just be over reacting. I would rather just have things fixed rather than leaving me stranded somewhere. I’m at the point of 100k where things are going to start breaking and I’m just trying to stay a head of the game.
Also I don’t know the last time the coolant was flushed so figured I’d do it next week on my days off along with my leaky valve cover gaskets.
Should I just by 3 gallons of coolant which make 6 gallons w/water? Or do you think I’ll need more?

#21

cstarky are you an S6 guy or an S8 guy. If your an S6 guy look at also replcement of the coolant tank. They tend to crack and they weep out coolant.

The Y is a good replacement the cap isnt a bad idea but its rare that that goes bad. If you want post a picture of the underside we can usually tell if its bad.

As for coolant it should be two full unmixed coolant stright coolant and two full of water. That should do it.

#22

I’m an s8 guy but the s8 boards are pretty lame so i hang out with you guys. I’ll get a picture of it tomorrow.
Thanks for the amount that i need. Like everyone else I’m trying to catch up in maintenence that the po doesn’t ever do.

#23

being an S8 you wont have some of the issues the S6 guys have. Your coolant container is in the inner fire wall right on the driver side so you will be fine there. I dont even think you have the coolant Y issue with how your coolant lines are run.

#24

Awesome thread guys. I just returned from the garage after digging into the passenger side trying to find what appears to be a minor coolant leak. I can see some remnants ever so slightly under the expansion tank with the airbox out - but I’m talking small little drips. The expansion tank looks like it needs to be replaceed; there are some some hair line stress marks. One of the bottom hoses looked pretty suspect - but I’ll need to pull the expansion tank to 100% confirm. Something similar to the video Scott made above seems possible to me. The area on the passenger side that meets with the front apron cover - the smaller apron that can stay on with the front cover removed near the downpipes - is wet, but there is not pooling below.

In addition to looking into the coolant issue over the weekend I also changed the oil. When going for a quick test drive today - first time out - there was a sudden pop and then a tat-tat-tat when I downshifted and laid on the gas. Scared me! I pulled over and there was a bit of smoke from the back of the engine bay. The performance was fine and whatever burned off coolant (I hope) maybe oil seemed to disappear.

I returned home, inspected, checked the torque on the oil filter. All seemed fine. Just a little more worried possibly something else could have caused this odd noise and dark gray smoke. :-\

Plan to order a new expansion tank, y connector, bottom house and complete flush with g13 once I confirm the location of the leak.