I've searched a lot of online sources and I've not come across a proper A6 C7 3.0TDI expansion tank replacement guide. Loads of other models and different size tanks with slightly different methods on different engine sizes, so I hope people will find this useful.
You'll need:
A pick tool, a T20 torx screwdriver, a turkey baster, a clean container like a measuring jug and kitchen roll.
Ultimately, there are only 2 hoses, a torx screw, a locating part with rubber retaining bung, a main hose under the tank and an electrical plug to disconnect.
Make sure your engine is cold and twist the expansion cap off. Get a new, cheap turkey baster and draw out your existing coolant and put it in a clean container/measuring jug. Cover it up and put it somewhere safe so it remains clean. I found quite a few specks of contaminants in mine so I just reused the clean stuff and topped up at the end. Put the cap back on the tank.
The next thing is to pick out the metal retaining clips from the two hoses. Just use a metal pick and bring it upwards, then pinch the pin with your fingers and twist a bit and pull out. Be careful how you do this, they're quite fiddly and you don't want to lose them in your engine bay.
You can then just tug the hoses out and pull them to one side.
Unscrew the one T20 torx screw and then you'll be able to pull the whole tank up from its locating part with rubber retaining bung, which sits next to the main, larger hose underneath. You will need to take this rubber bung off later, and out it on your new expansion tank.
Below are pictures of the tank removed to give you an idea of the bung and main hose entry point so you know what to expect.
At this point, it's only this main hose and the electrical plug (on the right) that's holding the tank in place. Although the main hose is relatively short, you can tease it upwards and bring the whole tank up to get a better view of the connection point.
Unless you were using an actual syringe, there will be some coolant left in the expansion tank which is why the next step was to get a big bunch of kitchen roll and stuff it down and around the main hose, under the connecting point.
To disconnect the hose there is another, larger metal retaining clip just like the smaller hoses, to remove. Again, be careful how to do this, as it's trickier to get to it than the other smaller clips previously removed. I used a magnet taped to a screwdriver to make sure I didn't lose it.
Once the clip is out and put safely aside, you'll find that the tank is properly wedged into hose. I had to use a flat head screw driver to help pry it off by pushing the outer hose down with the screwdriver, while simultaneously pulling up on the tank.
As expected, a load of coolant came out when the tank came away and you might want to get some more kitchen towel down there.
At this point you'll be able to turn the tank over and remove the electrical plug and the tank is then free.
Now take the rubber bung off the old tank and put it on your new one.
My old one was absolutely filthy and I couldn't actually see the liquid level against the 'min'/'max' levels.
My old part number ended in 'J' but the new part ended with 'AH' but they were exactly the same. For reference, the part number is...
Fitting is in reverse, just put your coolant back in and Bob's your uncle and Fanny's your aunt, clean new tank.
One last tip, make sure you push the smaller hoses in all the way. In my eagerness to compete the job, I made the mistake of only putting them in partially, took a short 5 mile drive and when I got home, discovered the pressure had took out one of the hoses and pretty much emptied the whole tank into my engine bay... So much for stuffing kitchen roll to save coolant going everywhere!
Anyway the point is kids, make sure you've got it on properly otherwise you'll shoot your load everywhere...
You'll need:
A pick tool, a T20 torx screwdriver, a turkey baster, a clean container like a measuring jug and kitchen roll.
Ultimately, there are only 2 hoses, a torx screw, a locating part with rubber retaining bung, a main hose under the tank and an electrical plug to disconnect.
Make sure your engine is cold and twist the expansion cap off. Get a new, cheap turkey baster and draw out your existing coolant and put it in a clean container/measuring jug. Cover it up and put it somewhere safe so it remains clean. I found quite a few specks of contaminants in mine so I just reused the clean stuff and topped up at the end. Put the cap back on the tank.
The next thing is to pick out the metal retaining clips from the two hoses. Just use a metal pick and bring it upwards, then pinch the pin with your fingers and twist a bit and pull out. Be careful how you do this, they're quite fiddly and you don't want to lose them in your engine bay.
You can then just tug the hoses out and pull them to one side.
Unscrew the one T20 torx screw and then you'll be able to pull the whole tank up from its locating part with rubber retaining bung, which sits next to the main, larger hose underneath. You will need to take this rubber bung off later, and out it on your new expansion tank.
Below are pictures of the tank removed to give you an idea of the bung and main hose entry point so you know what to expect.
At this point, it's only this main hose and the electrical plug (on the right) that's holding the tank in place. Although the main hose is relatively short, you can tease it upwards and bring the whole tank up to get a better view of the connection point.
Unless you were using an actual syringe, there will be some coolant left in the expansion tank which is why the next step was to get a big bunch of kitchen roll and stuff it down and around the main hose, under the connecting point.
To disconnect the hose there is another, larger metal retaining clip just like the smaller hoses, to remove. Again, be careful how to do this, as it's trickier to get to it than the other smaller clips previously removed. I used a magnet taped to a screwdriver to make sure I didn't lose it.
Once the clip is out and put safely aside, you'll find that the tank is properly wedged into hose. I had to use a flat head screw driver to help pry it off by pushing the outer hose down with the screwdriver, while simultaneously pulling up on the tank.
As expected, a load of coolant came out when the tank came away and you might want to get some more kitchen towel down there.
At this point you'll be able to turn the tank over and remove the electrical plug and the tank is then free.
Now take the rubber bung off the old tank and put it on your new one.
My old one was absolutely filthy and I couldn't actually see the liquid level against the 'min'/'max' levels.
My old part number ended in 'J' but the new part ended with 'AH' but they were exactly the same. For reference, the part number is...
Fitting is in reverse, just put your coolant back in and Bob's your uncle and Fanny's your aunt, clean new tank.
One last tip, make sure you push the smaller hoses in all the way. In my eagerness to compete the job, I made the mistake of only putting them in partially, took a short 5 mile drive and when I got home, discovered the pressure had took out one of the hoses and pretty much emptied the whole tank into my engine bay... So much for stuffing kitchen roll to save coolant going everywhere!
Anyway the point is kids, make sure you've got it on properly otherwise you'll shoot your load everywhere...
