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Audi A4 Rear Coolant Flange Replacement

Prior Experience: none required
Cost: approx. $60
Time: aprrox. 3 hours

Discuss this mod - Here
NOTE: All pics are hyperlinked to higher resolution versions.

A very common issue with the 1.8T is a coolant leak at the rear of the engine. This is almost always caused by an issue with the rear coolant flange. This flange is right at the back of the engine just in front of the firewall - it is plastic, and the heat cycling apparently causes it to fail early. Replacement at a dealer can be upwards of $600, but you can DIY for about 1/10th that

Now there are about a dozen ways to replace this part - this is by no means the only way to do it. The method I took was 'more work, less frustrating' - which means I removed parts you dont HAVE to remove, in order to make room for my hands, and see what I was doing. This is how I did it.

 

SUPPLIES - The supplies for this are pretty simple. You need a few simple hand tools, and then of courrse the coolant flange. The flange can be purchased at the dealer for $28 bucks - you can refer to the dealer catalog to find the part

To the right you can see the flange on the top - the tools are some picks, a magnet, some pliers and a pair of vice grips may be useful.

  Audi A4 Rear Coolant Flange Replacement

You should first try to see if you can see the coolant flange - it is behind the engine towards the firewall. You probably won't be able to see it, but it's back there. The picture on the left shows how it is oriented in the car. It is secured to the engine via two bolts. There are two hoses that go to it, and one coolant temperature sensor.

The picture on the right shows approximately where it is located - with the arrow pointing at the coolant temperature sensor.

Audi A4 Rear Coolant Flange Replacement   Audi A4 Rear Coolant Flange Replacement

 

In order to minimize the mess this will make, I recommend you drain the coolant.

To drain the coolant, look for the Coolant Sensor on the driver's side of the vehicle down below the headlight. It is easiest to access this with the car on ramps. There is a clip holding it into place. You remove the clip and pull the sensor out. The coolant will start pouring out - so have a bucket ready

 

B6 Audi A4 - Big Turbo Upgrade Install APR Stage 3 Coolant Sensor

  B6 Audi A4 - Big Turbo Upgrade Install APR Stage 3 Coolant Drain
 
     
 
Audi A4 Rear Coolant Flange Replacement  

Obviously if the part is hard to see, it will be hard to work on. This is why I took a lot of things out of the way - The goal was to remove everything that crossed over in the back of the engine.

I started the process by unplugging all of the ignition coils to get the harness out of the way. You have to unplug each of them, and remove the ground wire from the valve cover.

 

Next you should remove the hoses for the crank case breather. There are a few hose clamps that are one time use - you can remove them using a flathead screwdriver and a light tap with a hammer. I will try to find a picture that shows the technique.

Once you get the hose clamps off, I suggest you run a pick/flathead screwdriver around the hose to seperate it from the valve cover - this is true for all the coolant hoses, etc. Running a tool around the inside of the hose will make removing the hose much easier once you start pulling on them.

Audi A4 Rear Coolant Flange Replacement  

Audi A4 Rear Coolant Flange Replacement

 

Next I removed the injectors and moved the fuel rail out of the way. The inectors simply unplug, the fuel rail is bolted down in 2 spots with socket head screws - just use an allen key to remove them

Audi A4 Rear Coolant Flange Replacement

 

Audi A4 Rear Coolant Flange Replacement

 

I decided that I wanted to push the fuel rail all the way out of the way - there are two clips along the firewall that you have to undo. Unfortunately, they are not very easy to remove - you have to use a pick and a screwdriver at the bottom of the clips to remove them. I don't think there is anyway I can explain how to do it - I think you will understand when you look at the clips.

 

Audi A4 Rear Coolant Flange Replacement

 
The rear of the engine should look like this now that you have cleared some room   Audi A4 Rear Coolant Flange Replacement

 

Audi A4 Rear Coolant Flange Replacement   Now that you can see the rear coolant temp sensor, you want to unplug the sensor. The harness has a simple clip on it to unplug it.

 

At this point I chose to remove the coolant sensor - when you do this, additional coolant will come out. To remove the sensor, you remove the retaining clip (pictured to the right) and then pull the sensor straight out.

  Audi A4 Rear Coolant Flange Replacement

 

Audi A4 Rear Coolant Flange Replacement   In order to get my hands on the flange bolts, I had to keep removing parts. I removed the hose going to the combi valve to get some additional room.

 

With this hose connected, you can reach a wratchet around to start unbolting the two bolts that hold the flange in place. It is impossible to get pictures of this, but the first bolt that comes out looks like this:

  Audi A4 Rear Coolant Flange Replacement

 

Audi A4 Rear Coolant Flange Replacement   Now you can disconnect the lower hose. It has a metal retaining clip that you can remove with a flathead screwdriver. Some people recommend doing this before you remove the bolts to the flange so that you can have some leverage to pull on the hose. I found this unecessary as long as you do as I said and run a tool around the inside of the hose before you pull on it.

 

At this point you should have the coolant temperature sensor out, the two bolts that hold the flange in place out, and the lower hose out. All that should be holding the flange in place is the rightmost hose. For me, it was easier to remove the other end of the hose instead of removing it where it attaches to the flange.

 

This is what I mean -I removed the flange like this:

 

So instead of disconnecting the hose at the flange, I did it at the other end.

  Audi A4 Rear Coolant Flange Replacement

 

To do this, I just moved the hose clamp upwards like this:

  Audi A4 Rear Coolant Flange Replacement

 

And then disconnected this small hose to slide the assembly out. Again there is a one time use clamp here that you have to battle - I used the screwdriver/hammer method and held the clamp in place with a pair of vice grips to prevent it from spinning. Once you do this, the flange should be free.

  Audi A4 Rear Coolant Flange Replacement

 

Now you should have your assembly out. This is most of the work. From this point you just have to swap the part and reverse all of your work.

Once you get the new part in, you will have to refill the coolant - don't forget to plug in your coolant temp sensors!

  Audi A4 Rear Coolant Flange Replacement

 

The coolant fill/burp process is a bit lengthy.To start, you want to fill the reservoir up with coolant - it should take quite a bit - approximately a gallon or so.

 

Audi A4 Rear Coolant Flange Replacement   I then suggest you fill coolant into the upper coolant hose - there is a spot you can fill circled on the left. This will put coolant up high in the system where it likely is not.

 

Once the reservoir and the coolant hose are filled, you can start the car and monitor the coolant system. You will likely hear the fans come on, etc. Let the car warm up while keeping an eye on the coolant - turn your heat on high in the cabin.

 

The coolant system will be filled with air bubbles. Your goal is to get them out.

The air will want to travel to the highest point in the system. Audi has made an air drain point in the upper heater core hose. This is next to your battery. The arrow on the right shows a hole in the hose that is used to bleed air.

Undo the hose clamp and back this hose out a little until the opening allows air/coolant to come out.

  Audi A4 Rear Coolant Flange Replacement

 

Audi A4 Rear Coolant Flange Replacement  

You should eventually see some coolant come out. Once you do, put the hose back in place.

Turn the car off and slowly open the reservoir tank. You may have some bubble come out of the tank. Fill the tank as necessary.

 

From this point you want to keep running the car with the coolant systen sealed, and then turn the car off and slowly open the reservoir to get it to bubble out. It will take many times (5-6) to get all of the air out. Take the car for some short drives, and then stop, open the reservoir and let the bubbles come out. Eventually you will stop seeing bubbles and your system will be ready.

 

That's all there is too it. Hopefully this can help you!


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