Audi A4 (B5). Coolant Flange Replacement

If you have been losing coolant, or had a coolant burning smell after a long drive, or just happened to look down towards the back of the engine in between the firewall and noticed some pink crusting; then it's most likely time for a coolant flange job.



Picture by Andy TN showing some pink crust

The coolant flange holds the ECT (Engine Coolant Temperature Sensor) and is connect to the back of the engine head. It's a simple but semi hard to reach job but it's definitely DIY.

Let's get started:



Old vs. new. This side is the R side that will connect to the big black coolant pipe. Make sure you have a gasket in there



Coolant flange is semi installed. It's hanging in there loose



This side shown is the side that will attach to the engine, make sure that the gasket is installed and not torn... this is a leak area



The new flange with the temp sensor installed but no gasket between flange and engine



ETKA explosion diagram of the coolant flange and its connections



Some of the old coolant flanges will only have ONE port. The new ones that are sold come with a second port, that is seen PLUGGED in this picture. Make sure you have either an old temp sensor or the dummy plug from the dealer to fill the second port.

OK so now that you know how the coolant flange looks and where it connects to its time to get dirty:

You will loose some coolant during this procedure; it is also a good idea to replace the ECT as well while you are doing this.
You could either drain the engine coolant at the water pump or just leave whatever you have in there and see how much comes out.
I did the replacement on an engine that had all the coolant drained and replaced with brand new G12. Either way, make sure that the Engine is COLD or you will get burned.

Disconnect the cable leading to the ECT by squeezing the metal and pulling it off. You can leave the ECT in the flange or remove it. To remove it pull the small plastic U shaped clip out towards the firewall and then pull up on the ECT. You will have some coolant coming out right now.

I can't remember for sure if I had 6mm hex bolts of 8mm ones. But you need to remove 2 bolts that attach the coolant flange to the engine and another 2 that attach the flange on R side (looking from the front) to the black hose.



The picture to remind you. After you have those bolts loose you will have some more coolant come out. Pull the flange away from the engine block and also out of the black hose. The only connection that is left now will be the bottom hose.

In order to remove the bottom hose from the flange you will have to pull away a clip from the hose that will be on the flange. Make sure that you try to catch this clip as it will be flying away; it's very small and hard to find. After you have pulled the clip, hold the hose with one hand and pull on the flange with the other hand.
The flange will pop out with enough force.

Take your new flange and transfer the dummy plug and or new ECT from the old to new if needed.
You hopefully have 3 or 4 O-Rings depending on the flange. One O- Ring goes in between the flange and the engine, the other one goes between the flange and the black hose and the 2 other ones are for the ECT and the dummy plug.



Installation is in the reverse order. Make sure that when you tighten the bolts back up so just barely hand tighten them until everything is connected. Tighten them down a little bit at a time so the flange is not crocked installed.
Replenish the coolant lost, start the engine and check for leaks.

When i removed the old flange I didn't see any physical damage to it, so it might just be the O rings that are failing.

Good luck!