Audi Oil Cooler Leak – A Common Issue With The Belt Driven 4.2l V8

Audi’s models are often considered the best of the best when it comes to luxury sedans. The cars made by this brand were always a sign of power and prestige, but like any other car out there, they have their weak spots, too. One such issue is the Audi oil cooler leak that occurs in one of their most popular models — the spectacular pre-2006 4.2l V8. This engine is considered a better choice than its rather similar counterpart found in the B6 and B7 A8 series not only because it had a timing belt, but because it lasted a lot longer than its successor.

Join us as we go through the process of fixing the Audi oil cooler leak issue. We’ll go over the basics, and then dig into the more technical stuff!
audi oil cooler leak repair
Article updated on 11/10/21. Original publishing date 02/26/19

What Is an Oil Cooler?

An oil cooler is one of the essential parts of any performance or heavy-duty vehicle. Not every car has an oil cooler. For some, the radiator is more than enough to keep fluids at optimal working temperatures. On the other hand, the Audi 4.2l V8 engine has a lot of power and requires a fully-functional oil cooler to run smoothly even if it’s driven without using all the horsepower it has to offer.

As the name suggests, an oil cooler is a part that’s used to cool down the engine oil. In most cases, it’s a component that doesn’t require a lot of attention. Regular maintenance and oil changes will keep the oil cooler in good condition, but you should still check for leaks once in a while. There are parts of the cooler that need to be replaced with age, but aside from that, only mechanical damage can cause issues.

How to Diagnose An Audi Oil Cooler Leak?

audi oil cooler leak service position

There are a couple of symptoms to look for if you’re suspecting the oil cooler fault on your Audi. The things you should be looking for are:

  • Oil leaks under your car
  • Decreased engine performance
  • Stronger vibrations
  • Engine is overheating
  • Oil contaminated with coolant or water
  • Expanded radiator

If you notice any of these while driving, it’s best to pull over and turn off the engine until you can get the car properly checked out at home, or at a shop.

Oil Leaks

An oil leak under your car can mean many things, including a potentially faulty oil cooler. An Audi oil cooler leak isn’t distinctive compared to an oil leak from any other part of the car except for the location. If you notice a leak, it’s important to find out where it’s coming from as soon as possible because it can save you a lot of trouble in the long run. The best place to start are the oil cooler seals, which tend to go out over time.

Decreased Performance

Decreased performance can also be a sign of a lot of faults, but it’s also something you’ll notice if there’s a leak in your oil cooler. If there’s a leak, the pressure of the oil won’t be the same, and it will directly affect acceleration and top speed.

Unusual Engine Vibrations

When it comes to engine vibrations, every car vibrates more or less, but if you start noticing your engine vibrating more than usual, there’s a chance that the cause could be a bad oil cooler. That being said, this particular symptom is rare on the engines we’re talking about here.

Engine Overheating

Engine overheating is a serious issue with several potential causes. When it comes to an Audi oil cooler leak, it can cause the engine to overheat because it’s not doing its job properly — cooling the oil. If you notice your engine overheating, park the car because you’re risking serious damage otherwise.

Contaminated Oil

The reason why it’s important to fix an Audi oil cooler leak as soon as you notice it is because the engine oil can get contaminated by coolant if the gasket is faulty. A few drops won’t have a large effect on the engine, but if there’s a leak, it means it’s constantly being contaminated with more and more coolant which dilutes the oil and neutralizes its lubricating properties. As you can imagine, this can cause serious damage to the engine.

Step-By-Step Guide For Fixing A 4.2l V8 Audi Oil Cooler Leak

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A lot of people are intimidated by the process of fixing an Audi oil cooler leak, and for a good reason. The location of the oil cooler is very hard to reach, and most people think that the entire engine needs to be removed from the car, since Audi states so in their shop manual. However, there’s a way of reaching the oil cooler without removing the engine.

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

Step 1 – Secure the Car

Before starting any work, make sure your car is secure, and the battery is disconnected. Before disconnecting the battery, make sure you find and write down your radio code in case you’ll need it after reconnecting the battery.

Step 2 – Reaching The Oil Cooler

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Because the oil cooler is located behind the thermostat housing, this is something you’ll need to remove, but not before you remove the alternator and timing belt. While you’re in there, it’s a good idea to replace the timing belt as well as the water pump and the thermostat.

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Five 8 mm bolts are holding the housing in place. They are known to strip easily, so we recommend having a spare set just in case. You’ll need four M10x65 and one M10x40 Audi hex bolt for this.

When you have a spare set of these bolts lying around, you won’t feel bad about doing what needs to be done to get the old ones out. In our 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.

Step 3 – Remove The Oil Cooler

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When you remove all the parts in front of the oil cooler, you’ll find bolts that you’ll remove by using the 8 mm Allen key. Before trying to unbolt them with raw power, try nudging them or even tapping them a few times with a hammer to get them to break loose. It’s common for these bolts to jam so try and be patient. Unfortunately, it’s very easy to trip the head of these bolts by forcing them.

If you end up stripping some of the bolt heads, you can use a 15 mm 12-point socket and a bit of hammering to remove them.

Step 4 – Find The Cause Of The Issue

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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 leftover pipe (usually about 1/4″ of a broken ring) from the engine block and don’t forget to get 3 required O-rings (077121437).

Step 5 – Put It All Back Together

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Once you’ve replaced the gasket, pipe, and O-rings, you should refit the oil cooler back to the engine block.

Finger-tighten the bolts before torquing them to 18 ft-lbs. It’s recommended to start at the far left bolt and continue to tighten the other bolts moving clockwise. Double-check all the bolts are torqued correctly.

After you’ve reassembled the oil cooler and fitted the rest of the parts that needed to be removed in the process, top up the mighty 4.2l V8, start it up and make sure to check for leaks. Always use the right oil and the right coolant for your car. If everything is done the way it should be, your Audi oil cooler leak should be a thing of the past.

Need Parts To Fix The Audi Oil Cooler Leak?

Although it sounds like something most people wouldn’t dare to try, fixing an Audi oil cooler leak on a 4.2l V8 isn’t as bad as people think.

Here at, we carry all the OEM parts you’ll need to do a fine job of fixing the oil cooler leak on your 4.2L V8 Audi! Just type in the make, model, and production year into the search bar, and you’ll get a list of all the parts that are made specifically for your car.

Posted in Audi, DIY How-To, Used Cars

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