Audi Oil Cooler Leak – A common issue with the belt driven 4.2l V8


Chances are when you see an Audi with the 4.2 badge on the back of it, you automatically think of the plagued issue of timing chain tensioner and guide issues. These problems are one of the later 4.2 engines that graced the B6 & B7 Audi S4 as well as a slew of other models, but pre-2004 for most Audi models (with exception of the Audi A8 that went until 2006) there was a very well built eight cylinder engine driven by a timing belt inside the engine bay. The later engines that experienced multiple catastrophic failures were due to a new timing chain system that wasn’t necessarily bad, but just didn’t like to go past 100,000 miles. Apparently, that is the benchmark for the word “lifetime” in cars.

Recently, I picked up an Audi S8 that needed multiple fixes to bring it “up to speed” and figured that this would be the perfect opportunity to help out the others wanting to get their hands on an older Audi. The first thing to watch for is coolant dripping from around the alternator housing. Because I stupidly checked the car out in the rain, I never saw the telltale drip that showed the dreaded Audi oil cooler leak! Breaking out the Audi manual for the car, the procedure is as follows: Put car in service position. Remove engine.

“Service position”

Ok, this just wasn’t going to happen just yet, so I did some digging to find a proper solution without having to remove the engine on the car I just bought. Looking at the engine bay and other pieces of the literal jigsaw puzzle, I concluded (correctly) that I could do the timing belt, water pump, and thermostat combo at the same time and get that peace of mind as this car had been sitting for some time now. Any of these cars with over five years of minimal use needs a timing belt as there is a lot of strain put on the system. The small tolerances spell immediate failure, as being off a tooth on the timing belt will mash your valves into a moving piston.

To get the access to remove the oil cooler and replace the offending pipe, you need to remove the thermostat housing…which is behind the timing belt. I will get into the timing belt procedure in a different article, but for now, take a look at the room with the housing gone and the time (and cursing) ultimately saved is worth every minute spent in tearing down the timing belt assembly.

You will also need to disconnect and remove the alternator.

*Make sure you have your radio code before disconnecting the battery!*

This procedure will work on any D2 Audi A8 and S8, early D3 A8 4.2 up to 2006, and the 4.2 C5 A6 and S6.

There are five 8mm bolts that hold the housing in place that will strip out very easily as you attempt to remove them. For the sake of your sanity, I suggest ordering a new set before you even start the job. (Audi Hex Bolts Four – M10x65 and One M10x40) Once the new ones are in hand, you will have no qualms in doing what needs to be done to remove them once they strip out. In my experience, the method to remove the “tough” bolt in the upper far left, is to use a small 2″-3″ extension with a swivel socket and then a larger 6″-8″ extension and a 3/8 drive long handle ratchet.

The other bolts will require an 8mm allen key with a ball on the end as they never really fit straight on. DO NOT FORGET TO TAP THE BOLTS WITH A HAMMER AND PUNCH BEFORE REMOVING. It helps knock the frozen bolts loose.

If (and when) you strip the bolt head, you need a 15mm 12 point socket to hammer onto the bolt with a 3lb mini sledge. You might reel in horror while hearing this, but it has proven to be the absolute best way for me to remove these bolts.  The metal is very soft.

Once the assembly is loose, you will see the “figure 8” gasket that needs replacing (077115441) as well as the broken oil cooler pipe (077117411A) that is the source of your current trouble. Be sure to remove the left over pipe (usually about 1/4″ of a broken ring) from the engine block and don’t forget to get 3 required O-rings 077121437.

Audi Oil Cooler Leak

Use a bolt to screw into the plastic piping to remove the broken pipe fragments.  That should all work very nicely in keeping any coolant seepage at bay. Lubricate the o-rings and refit the assembly to the engine block.

First finger tighten the bolt and proceed to torque the bolts to 18 ft lbs. Start at the upper far left bolt and work clockwise until complete. Recheck the torque again to make sure everything is uniform.

After reassembling the timing belt assembly and other parts, top off with fluids and start the old 4.2 up while looking for leaks. As long as you checked your work and torqued everything correctly, the car should be fine and you won’t have to worry about another Audi oil cooler leak (or timing belt) for a very long time.

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Posted in Audi, DIY How-To, Used Cars

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