Oil Cooler Oil Leak

A6 All/ S6 All
#1

Hello.

I did quite a bit of work after I purchased my 2008 S6; (valve cover gaskets, oil filter housing o-rings, valve cover gaskets, etc).

The last think that I did was reseal the oil pan as it looked like it was leaking.

But I seem to still have the oil leak. I think it is the oil cooler on the passenger side of the engine. From what I can see, that is the only thing that could be causing the leak.

I am going to change out the o-rings on it. From the Bentley manual, it says you have to remove the radiator, then the belt and belt tensioner, the the alternator, then a bracket, and then you can get to the oil cooler.

How many o-rings does it require? Also, do you need to drain the oil to do this work? Any thing else that I might need to know?

Thanks.

#2

there are just two o-rings to the oil cooler. i bought some replacement o-rings from ECS but the actual parts did not match, so i’d check with your local dealer or audiusaparts.com (it’s run by a dealer IIRC) to make sure you get the right ones.

you’ll need to remove the coolant hoses to the alternator and oil cooler, so i’d strongly recommend getting a set of hose-clamp pliers. it will make your life 1000x easier.

the bolts on the oil cooler are t30, but the rear-most bolt on the cooler is almost impossible to see/access. i used a borescope to help guide my my socket wrench/t30 to the bolt head. the bolt itself is easy to feel with your fingers, but the space is so tight it’s hard (impossible?) to get both hands and a wrench in there at the same time.

the generator mounting brackets require triple squares - M8 and M10, or M10 and M12. can’t remember offhand.

i had my oil drained at the time, so i’m not sure if you do need to drain the oil. most of the oil should be in the pan, but the cooler is going to some oil in it (plus coolant, too).

#3

Great post fenixgoon

To add to what he mentioned. Expect to see the coolant like he said. Coolant runs though the oil cooler to cool the oil. take some time flush out the cooler and if you haven’t already its a great time to flush the coolant.

#4

Thanks for the info. I think I have almost everything that I need. I may look into getting a borescope if it will help with that blind bolt.

I will probably also change out the serpentine belt at the same time while there is room and will definitely do a radiator flush.

Other than this oil leak, the car has been running very well since I changed the intake manifold and changed several of the gaskets. Has been very reliable.

#5

If you have the wheel off and the fender liner pulled back, you can just see the head of the bolt if you shine a light from the front of the engine between the coolant pipe and the bottom of the oil cooler.

#6

with the radiator out of the way, changing the serpentine belt is super easy.

and i completely forgot - if you’re on the original water pump, you may want to do that and/or the t-stat as well, since removing the oil cooler is basically the 2nd to last (official) step to removing the water pump. the bentley manual says to remove the front coolant pipe (last step before water pump), but it isn’t absolutely necessary (plus the rear bolt to the engine is pretty awful in terms of clearance/access) when removing the water pump.

#7

I think I have the correct O-rings for the oil cooler. Could someone verify that it is correct?

Part number is 079103121AD.

Thanks.

#8

That is the correct number according to oemepc.com
24 x 2.5mm

#9

Alright then. Got the 0-rings changed. HOLY SHIT!, that’s a lot of work and frustration to change out 2 simple rubber 0-rings. I really didn’t have any trouble getting to the bolt behind the oil cooler. You can actually just see the head of the bolt by shining a light from the front of the cooler to the back on the bottom. There is a narrow slit. Made removing and installing the bolt a lot easier.

The hard part was removing and getting the hoses off and then on for the alternator. I had the luck of one of the spring clamps one of the hoses breaking. The part where you squeeze the clamp broke and the clamp was gripping the hose still but the hose was not fulling on the pipe. No space to work at all. Finally got it but man it sucked.

Pretty sure this was causing my oil leak but I will monitor and see how it is.

https://photos.app.goo.gl/XxXDmTqh6LHd1zss9

https://photos.app.goo.gl/vhBPc6XggdK8gGj46

https://photos.app.goo.gl/ndC4cnuWrEQ9V9tN9

https://photos.app.goo.gl/s45dnueaQSK565Bv7

https://photos.app.goo.gl/5QzHSnrd1bMJT7yZ7

#10

Link to Google Album with a few pictures:

https://photos.app.goo.gl/YvKfQsNDFDcFEtpo7

https://photos.app.goo.gl/YvKfQsNDFDcFEtpo7

#11

You have to be somewhat “gentle” with that short 90 degree hose that connects to the alternator. When I did my oil cooler o-rings a couple of years ago, I did not have the locking hose clamp pliers that I have now. I had to wrestle with those clamps using various other tools. I must have weakened the hose somewhat as three months later that hose failed while I was on a road trip about 200 miles from home.

#12

I ended cutting both of them and them put in new ones. Made things 10x easier, and seemed to make sense to me at the time as these hoses were already 100k+ miles old.

#13

That short 90 hose did make things difficult. The hose was still in good condition so I hope is will hold up.

What I ended up doing to make things slightly easier for me was to unbolt the screw/bolt/hold-down that holds both of the fittings into the alternator. I then put the hoses in the proper position then the alternator and tightened down the hold-down on the backside of the alternator. Not very easy to do and hardly any room but it was easier for me.

#14

Quick update.

No more oil leak! Bottom of engine and the belly pan are both dry. Hopefully, it will stay this way for a long time.