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Oil Cooler repair


Old 02-03-2007, 03:28 PM
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Default Oil Cooler repair

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.
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Old 02-03-2007, 06:45 PM
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Default The one time I assisted with the removal of an oil cooler......

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).
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Old 02-03-2007, 08:32 PM
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Default 2nd ski's comments.

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.
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Old 02-03-2007, 08:59 PM
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Default Also good idea to replace all seals and gaskets while you are in there

<center><img src="http://pictureposter.audiworld.com/96745/oil_cooler_3.jpg"></center><p>these little seals and the plastic tubes are well known for failure
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Old 02-04-2007, 04:48 AM
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Default I had mine done @ dealer for $800. Only about $50 in parts...

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.
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Old 02-04-2007, 11:10 AM
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Default Good reading for a n00b like me Jim / ski / Grease, mental prep for what's...

...to 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!
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Old 02-04-2007, 11:52 AM
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Default skiracer assisted me on my oil cooler repair. I feel your pain....

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.
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Old 02-04-2007, 05:29 PM
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The post-facelift cars have the 40V engine, which hasn't seemed to have had this problem.
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Old 02-04-2007, 08:41 PM
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Default Re: Oil Cooler repair

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.
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Old 02-05-2007, 12:55 AM
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Default Right. Instead the 40V oil coolers put oil in the coolant when their O-rings get old

... 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.

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