View Full Version : Oil Cooler repair

02-03-2007, 03:28 PM
I'm a new member here...

Attempting to apply the article by Scot Danrich about servicing Audi oil coolers to a friend's 1997 Audi A8 Quattro. The only symptoms the car showed were a dropping oil level and oil showing up in the coolant. It was diagnosed by the Audi dealer as a blown head gasket, with an estimate of many thousands of dollars to repair.

However I gave the car a compression test and compression was good on all cylinders. Never having seen a head gasket blow only between an oil gallery and the water jacket, without blowing to a cylinder, I had doubts about the dealer diagnosis and began looking elsewhere. Could be a cracked head or block, but once I discovered there was an oil cooler that has both oil and water connected to it, that became the next logical culprit to check out.

I started doing the procedure outlined, but am now stuck. My problem is Scot's article seems to be based on having a lot of other stuff removed from the front of the engine, the radiator, probably the subframe, etc. I only removed what it said to, including the air filter box and the alternator. I have the oil cooler completely unbolted and free of the block, but can't get it out of the engine compartment. It's trapped between the exhaust manifold and a large tubular frame element that supports the front bumper. I can wiggle the cooler around and rotate it slightly, but can't get it out.

The article mentions unbolting one of the engine mounts and jacking up the engine on that side to provide better access to that area. I did that, but jacking on the engine just raised the entire car, even with that engine mount disconnected. There appear to be more mount points, specifically it looks like there's one that attaches to the frame in the region below the right headlight. So it looks like there may be a one or more steps missing in the procedure, and more things that need to be removed.

If anyone has experience with removing and replacing the cooler with the engine, radiator, fans, etc remaining installed in the car, please help.

PS: I struggled for about an hour to drain the radiator using the petcock -- with the tranny cooler lines going right in front of the valve, couldn't get a straight shot at all with several different screwdrivers, and the valve was very tight too -- only succeeded in damaging the slot in the blue plastic. Finally just gave up and pulled the lower radiator hose, making quite a mess.

02-03-2007, 06:45 PM
it was not part of a timing belt replacement. We successfully removed the cooler without removing an engine mount or raising the engine. With the coolant pipes, oil filter cover and oil filter removed (I assume you have done this), we removed the cooler by rotating/wiggling it out through the bottom gap. It is a bit of a chinese puzzle, but it can be done. Pay attention to how you get it out- it has to go back in ;-) Keep at it- it can be done (it was a 1998 A8 that we were working on, so it should be identical to the one you are on).

02-03-2007, 08:32 PM
I did the tubes on mine, at the same time I did the timing belt, thinking there would be synergies. In reality, there really aren't any.

The back bolt that is high on the oil cooler is a real bear. You can barely see it, from up top, with a very carefully placed inspection mirror. I was able to remove it with two extensions and a u-joint, and the appropriate Torx bit and a rachet handle.

Also, I did not have to lift the engine in the sub-frame, to remove mine.

Always Overcharged
02-03-2007, 08:59 PM
<center><img src=""></center><p>these little seals and the plastic tubes are well known for failure

02-04-2007, 04:48 AM
2 years later had the timing belt (etc) done and bought parts to do the repair again because I thought they would be working near the oil cooler. Was told it was alot more work and they didn't think it was worth doing. I have all the parts necessay (about $50 worth) which they had to order if someone needs them I'll ship them for $40. Mine was a 1998.

02-04-2007, 11:10 AM come.

ASSuming much of these 'gems' are same for '01 //S8?

Hmmm, sounds ahem fun - "can't wait". Hoping the culprit will be obvious with bumper / alternator removal. Bumper sounds easy as me C4; any alternator secret handshakes to keep in mind?


Anyone got a spare belly pan layin around? Again ASSuming they're all one in same '97-'03 or would that be a dangerous ASSumption? PO's "wife" (hey it's always the wife right) apparently er disposed of it - evidence the slight tear in the underbumper black skin from being kerbed and backed out after. YOINK!

02-04-2007, 11:52 AM
We could not work the oil cooler out after I had it unbolted until we removed the timing belt cover from the engine on the passenger side of the engine. This finally gave sufficient clearance to work the oilcooler out and go back with all new o-rings, figure 8 oil gasket and new plastic pipe. Use a good torque wrench with appropriate extensions and wobble-joints to re-mount the oilcooler.

02-04-2007, 05:29 PM

02-04-2007, 08:41 PM
Thank you people for the comments. Turns out a couple of you were right, I tried turning the unit every which way for about half an hour without success. Once again tried jacking on the engine on the passenger side, and it worked! Apparently even though it looked like the whole car was raising, the frame must flex just a little bit, which is enough. I may have been jacking too near the center of the engine before, not far enough over toward the passenger side.

After getting the cooler off, found the plastic pipe was broken just like the one shown in the article. The O-ring and the end of the pipe had to be fished out of the block, and the O-ring was warped like a potato chip! I can see how this would allow oil to leak out onto the ground, but haven't yet figured out how this would allow oil into the coolant. May have more than one problem?

With the cooler out, I'll now try to find someplace that can pressure test it somehow. I'd think rubber stoppers that fit the coolant passages, one with a compressed air fitting on it, should do the trick.

There's a housing on the inside, that I assume encloses some kind of heat exchanger. It's held on with about a dozen Torx screws. Should I take it apart? I didn't get the gaskets for that.

02-05-2007, 12:55 AM
... and are harder to remove because the engineer who arranged the coolant pipe between the back of the engine and the side of the oil cooler is a sociopath. I posted in September 2006 some observations about the job.

The O-rings lasted less than 110,000 miles on my car, so I'm changing them every time I change the timing belt from now on.


02-05-2007, 05:42 AM
..."This is when I started to want a simple Citroen SM. The back of the 5V 4.2 engine is a dumping ground of misanthropic cooling system design." and.. "the engineer who arranged the coolant pipe between the back of the engine and the side of the oil cooler is a sociopath" sure are um, 'encouraging'.

Oh joy!

Sounds as if best to have backup car so this job can spill into mutliple daze is a good idea - goody then I get to fix the fuel line leak in der ur4kq. Sun never sets in my world I tell ya.

Appreciate the details. $14/bottle G12 'til it gets warmer than oh say 4o like today, yeah.

Ah, then to move on to such fun things as rear main / trans prop shaft / front diff seals...


But the spacers look good at least 8-).

Anyone make any sorta D2 "Depends" I wonder? Hmmm. I just call it AudiSweat, really...

02-05-2007, 05:47 AM
<center><img src=""></center><p>Not worth pressure testing it, unless you're just curious. Even if it tests as "good", you'll want to replace them anyway.

When I had mine done a year or so ago, they replaced the little plastic pipe, and the seals between it and the block and cooler. But they didn't replace the internal seals, (#18 on that diagram, IIRC) and I ended up having to have those replaced later, at almost the same cost as the initial repair.

They cut me a break on the labor, since they're getting real good at that procedure! (yes, I probably could have pushed harder since they probably should have done the internal ones the first time, but live and learn, I guess...)

02-05-2007, 09:53 AM
I guess with the pressure test I just wanted to absolutely rule out before making any changes that the leakage was in fact inside the oil cooler, and not a cracked block or something. But I suppose another way to look at it is if the cooler is completely rebuilt and the problem still exists afterwards, I'm not any worse off than I was before anyway.

Thanks for the response.

02-05-2007, 10:07 AM
Good to hear this is a symptom others have experienced, so I know I'm not chasing a ghost. It looks like I'll need a lot more gaskets and parts. If I have to completely rebuild the oil cooler, now I'm wondering if it wouldn't be better and eaiser to just order a complete replacement unit from Audi, rather than all these piecemeal replacement parts -- everything would be done exactly right, all gaskets in the right place, screws torqued to factory specs, etc. Maybe they've even updated the design to eliminate or at least reduce the chances of this problem in the future.

On the other hand, maybe I care more about this being done right than someone on an assembly line in Germany. Any comments on that?

02-05-2007, 10:54 AM
... eliminate or at least reduce the chances of this problem in the future."

Bwhahahahahaha. Good one! It's an Audi, remember.

Yer funny tho 8-).

More like "maybe Audi decided to stop making replacement parts cause they want you to lease a new (disposable) //SLine" and blatantly snubbing their "roots" while paradoxically at the same time using Sport Q's and Michelle Mouton in all their latest marketing hype.

Or something, and stuff.

02-09-2007, 02:09 PM
What about the heat exchanger itself, #19 in that diagram? (part #077 117 021 J marked on mine) Without doing some kind of pressure test, how do I know that doesn't have pinholes in it or something? (not that it matters, the dealers don't list a replacement for that part in their system.)

Incidentally, I've been to several radiator shops and none seem to be set up for pressure testing something like this. So I guess I replace all the seals and gaskets, and hope for the best!