Audi A6 (C5) Avant, 2004 (3.0L, Quattro)
145,000 Miles

There seems to be a leak somewhere, can't seem to identify the exact problem. It's been over month. I'm suspecting fluid from somewhere in the transmission and possible condensation present in the exhaust (look at the condition of the flex pipes, gross). Can this be something else? I understand leaks are quite common in our Audi's. I would like to get to the bottom of this and address these problems as soon as possible. I'm on an extremely tight budget. I hope I can sort this out.

I have fault codes (Bank 1 & Bank 2) pertaining to the catalytic converters, which I've been reluctant to change since the day I received the vehicle (March, 2014), I've been told that as these vehicles age, the ECU tends to pull a lot of false positives on certain components.

The flex pipes were changed less than a year ago by a nearby mechanic (August, 2014). Look at the condition now as pictured below, amazing, isn't it? Costed me over $220.

I've done a lot of work on this vehicle, but am on a tight budget now. My front tires and wheel balance are due for replacement in the coming weeks ahead, and don't want to over-spend.

Please let me know what you all think.
Thank you. I greatly appreciate everybody's guidance and support.

Back in early-May,







First week of June,



Getting to the bottom of this,

Yes I did. I cleaned the best I could. Pretty tight quarters, should have kept the car on jack stands, but chose to go with ramps for the sake of convenience. []

Here are the pictures,

Starting with the Exhaust System,




















[URL=http://s1088.photobucket.com/user/arjun90/media/DSC00996.jpg.html]

Transmission-Related Components,

 

 

I am almost certain that leak is coming from the rear output shaft seal on the transmission unit. More specifically the distributor gear housing at the very back of the transmission which links the transmission to the rear wheels.

The good news is that this is a ~10/20 dollar part. The bad news is that it's kind of a pain to do if it's going to be one of your first DIY jobs. As a somewhat beginner I would give this a 8 out of 10. If you've got some experience under your belt, I'd rate it 3 out of 10.

Really no special tools required, but you will have to drop part of the exhaust, remove some insulation material, drop the drive shaft, remove the drive shaft coupling with the splines on it, and finally remove the faulty O-ring. Installation is nearly the same, but in reverse. Be mindful of seating the O ring properly. You will need to use a piece of PVC pipe with the same diameter to push it in evenly or it'll just leak again. After everything is all put back together, you will need to re-fill the distributor gear with 75w-90 (I think) gear oil and call it a day.

Those flex pipes do look pretty bad for only a year of driving, without regard to the elements. I've seen cars that have 12 year old flex pipes that look better than those do. The mesh portion looks to be giving out already. There is an accordion-style joint below it, but who knows how long that will hold up. But if you only paid $220 to have that exhaust work done on an A6, then a year is plenty of time. I'm assuming you got used parts and just didn't know it/weren't told.

Actually... looking at those pictures again... they just welded new (used) flex pipes into the exhaust system and called it a day.

 

Thanks,

A technician at Audi's Part Center (over the phone) has mentioned to me replacing the seal wouldn't be a permanent fix and that I would need to also purchase the stub shaft on the prop shaft (>$300 part) along with a revised seal to permanently fix the leak. Does this sound reasonable? I'm in doubt because its another $300 to top it off.

Also, what are your thoughts on the transmission fluid pan?

Thanks again.

 

I am sure this is Audi being overly cautious and doing everything by the book. If they do a repair, they will cross their Ts and dot their Is so they do not have to do a repair again if for whatever reason that output shaft was deformed which would allow a leak to present itself again. There might be some legitimate concerns as to why they recommend changing the shaft, but I didn't and have had no problems. Me personally, I'd order the seal and replace it myself. It'll cost about 20 dollars if purchased online and if it doesn't work and you wind up having to replace the output shaft, then you're only out 20 dollars. Not the worst thing in the world.

As far as the transmission pan and the possibility of the gasket leaking, I would be more inclined to say that it might be the valve cover gaskets and cam chain tensioner gaskets leaking given what I see on the boxes, and how far up (and how wide) those stains go. These cars are known to develop leaks that look like what you're seeing.

The reason why you are seeing it on the transmission pan is because it's most likely being pushed back by the air as the car is being driven at highway speeds.

You will have to run your fingers along the valve cover mating surfaces and along the back side of the heads to confirm if that's where it's leaking from.

The C5 3.0 is an interesting engine given in many instances the timing belt service procedure requires you to remove the valve covers, and as a result change those gaskets again because they really should not be re-used or they will more than likely leak. So depending on when the timing belt was done it may or may not make sense to just do the valve covers.

Bottom line: Check your engine oil once a week to make sure it's at the right level and you won't have to address it right away. Given the amount of fluid leaking out from the output shaft seal I'd actually address that first since you can't exactly easily top off that fluid once a week if need be. Then I'd address the valve covers - assuming that's what's leaking, that is.

Good luck!

 

Thanks,
I have replaced the valve cover gaskets back in April, and there is no indication of a leak in that area. Also, the engine bay smells clean. This 3.0L engine doesn't have cam tensioners, interesting to note.
Not sure what else it could be.

The orange color is just the rust from the rotted flex pipes it seems.