First I would like to thank Tom Tuling and BrianC72gt for their write ups on the 4.2 oil cooler pipe replacement. This last week I have been tackling this repair in my friend's garage and would like to share a few tips to help make this job easier for anyone in the future.

audipages A8 Oil Cooler Removal and Reinstall

Oil cooler repair on 40v 2000 +A8 - LONG post..even for me - AudiWorld Forums

Some background:

I purchased a 2002 A6 4.2 for a price I could not say no to. The car came with some problems, mainly the coolant leak from the oil cooler. Prior to buying this car I also at one point purchased a 2000 A6 4.2 that was in a wreck and parted it out and planned to use the 4.2 to swap into my 2000 A4 2.8 avant but discovered the engine was too badly damaged in the wreck to use in my project car.

I once worked full time as an auto technician at a small mom and pop garage so I am no stranger to working on cars and handling tools.

The writes ups on the C5 A6 4.2 are very helpful, study them thoroughly.

I planned to do a timing belt service after the oil cooler pipe replacement so I figured it would be easiest to remove most of the front end. I removed the front bumper, headlights, hood latch, fan that on the outside of the a/c condenser, and a few other parts I am forgetting in order move the front clip out of the way and gain access to the front of the engine. I unbolted the a/c condenser and set it on the ground and was careful not do damage it while working. The C5 4.2 a/c condenser has hoses on both sides, unlike the 2.7t. By laying the condenser flat on the ground in front of the car I was able to swing the radiator and the rest of the front clip out of the way (I drained the coolant and unhooked the right side radiator hoses).

To gain access to the oil cooler housing I removed the airbox and alternator. From here I removed the right side engine mount. I also removed the front engine mount (not sure what to call it) that secures the engine about midway up with a bracket on the right side. This helped with visibility and only took a minute to remove.

The oil filter housing has five 8mm hex bit bolts that secure it to the engine block. Three of them are easy to find and remove. The one that is on top is hard to reach and was a pain in the *** until I decided to unbolt the left side motor mount and jack the engine up a few inches. I tried jacking the engine up with just the right side motor mount but was unable to gain access to the top bolt. With both engine mounts unbolted (and the right side removed) I was able to raise the engine enough and gain an eye line on the top bolt. I used a universal (swivel) 8mm hex bit socket with a short extension to remove the top bolt (the exhaust manifold make it impossible to get a straight shot at this bolt). The last bolt I removed was the one behind the oil filter (remove the oil filter before removing any bolts). Unbolting the left motor mount made it possible to raise the engine up several inches by placing a jack with some pieces of wood underneath the oil pan. Without the extra inches this provided it would have been way more difficult to unbolt the top bolt. Also, removing the front mount allowed me to see the bolt.

There is also a small, black, metal coolant pipe that is attached with a 10mm bolt. Remove the bolt and pry the pipe off from the housing. I also suggest replacing the o-ring which is not included in the oil cooler gasket kit.

I cannot stress enough how important it is to make sure the hex bit is fully seating into the bolt head before applying torque. The bolt that was behind the oil filter had some rubbery substance that did not allow the hex bit to fully seat (After removing the oil filter housing it appears that the previous owner sprayed some sort of rubbery gasket-like material where the oil filter housing was leaking coolant in a futile attempt to patch the leak). Had I not realized my bit was not going in all the way I would have surly rounded the head and made this job 100x more difficult. I got out the old mirror and work light and used a pick to removed the substance that would have ruined my day from the bolt head. I also sprayed every bolt with some silicone spray.

Once unbolted, freeing the oil cooler housing required some prying and pulling but eventually came free. I highly suggest removing the oil pressure sending unit before trying to pull the housing out. Not sure what millimeter wrench is required, but I used a 1" wrench and was able to remove it before trying to shove the housing back into the engine compartment. From reading the experiences of other users I feel that unbolting the left engine mount created a little more space and made it a little easier to slide the oil filter housing in and out a little easier. I still had to use a large pry bar and carefully maneuver the housing in order for it to slide back in but it went in with not much of a fight (I expected it to be hell from reading the other posts).

I used the metal coolant pipe replacement that some very kind and generous man designed and had manufactured and sells on eBay and some other websites. I got a gasket kit from ECS tuning for the oil cooler. The only special tools I used was the universal 8mm hex bit which I used to break the top bolt and the bolt that was behind the oil filter.

Well this was my experience, I hope these tips will come in handy for someone else.