2002 4.2 coolant leak...can't find source...pics
 

So my wife's 2002 A6 4.2 has a slowish coolant leak. What is really weird is sometimes it appears green when it is dripping, but when I use a white shirt or sock to suck it up off the ground, you can see the pinkish tone...anyways, I got under the car and I am having a very difficult time tracking it down...I did take some pics of underneath so you know where I am looking in the general vicinity.

First off, is the black pan to the right in the pic the trans fluid pan or the oil pan? I feel like an idiot asking, but I want to make sure...

Next, it seems to be wet ON TOP of that black pan, but I can't see anything dripping down onto it...it looks wet around the white caulk as well, which concerns me that it is leaking out of the block through that...

Is there a common problem that I should know about when it comes to leaking? The car has 75k and has been well maintained. Any help appreciated, although I know it is difficult to gauge in a post

Well, is the first pic a pan thats under the engine? LOL that looks like the 4.2L oil drain plug in the first pic, its a large allan bolt.

The only thing on the back of the engine block that could leak on a 4.2L is the rear crossover pipe, or a freeze plug. Most likely the crossover pipe. There is no auxilliary after run pump like in the 2.7T if you were wondering.

So the black pan on the right that takes up a lot of space on the first pic IS the oil Pan, and that is the oil drain plug? I just wanted to make sure...where is the cross over pipe located? Difficult to replace?

Trev

The crossover pipe connects both cylinder heads with coolant, and yes its a major pain in the ass to do. Well anything on the back of a 4.2L is hard to do. It may be best to have a euro shop handle this one, unless you have a weekend to kill tearing apart the back of the motor.

Oh and yes thats the drainplug, holds a crap ton of oil too.

gotcha....whatever seems to be leaking seems to leak it down on top of the oil pan...would this still be the crossover pipe location?

Yep, oh and i had a major brain blooper! I believe the coolant temp sensor is located back there on the 4.2L also! Definately check that out first, as that would only be a $40 repair. That should be behind the motor on the passenger's side, it usually sits on......of course the crossover pipe. Might be a pain to get at.

Leaking on passenger side?
 

If it is leaking down the passenger side of the pan, then it is the plastic one inch pipe that audi has decided is the best way to connect the oil cooler to the block. I am in the middle of changing that pipe myself on my 2000 Audi A6 4.2 ART engine. The plastic pipe has two o-rings on both ends and after time, gets brittle. When I took the oil filter bracket off, the pipe was broken at both ends. Its taken me around 4 hours to get at the pipe as you have to remove the oil filter bracket which also houses the passenger side engine mount.

Hey there, I have the same issue right now and Audi wants 3k to fix it....YES I laughed and drove off...however, I cant seem to find a picture or diagram of the oil cooler to the block. Does anyone have this? I do not have a manual (hey, I just got the car very recently) but plan on getting one after the holidays. That being said, if anyone can chime in and give me a link, etc to a picture, step by step, etc I would GREATLY APPR. it!!
Thanks in advance!
Chans

Hey im having the same issue with the coolant leaking on the passenger side of the block ...i went in to a local audi/vw mechanic shop to change the water pump and timing belt as well as pullies, rollers and tensioner, after taking care of all that 4 bolts to the water pump broke and had to be extracted with inserts....after finally removing the remainder of the 4 bolts that drilled out and extracted the upper hose to the radiator was leaking...now him facing a new leak and honestly want to know if the block may be cracked or leaking from corrosion i have tried and thought of every solution but @auditech79 will the coolant temp sensor really be a cause for the leak?