A4.B5.DIY.Engine.Cooling.CoolantFlangeReplace
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Background
If you have been losing coolant, or had a burning coolant smell after a long drive, or just happened to look down towards the back of the engine and noticed some pink crusting, then it's most likely time for a coolant flange replacement. The coolant flange holds the ECT (Engine Coolant Temperature sensor) and is connected to the back of the engine head. It's a simple but semi hard-to-reach job and definitely DIY.
(note by Bob Dunne 1/01/2010. I just did this on an '01 A4, 1.8T AWM engine. It is a LOT harder to do than it looks in these pics. I'm not sure which engine is shown in the procedure. The concept is as Andy describes but it's really tight. Couple of key points:
The bottom corner of the housing is sandwiched between the mounting point for one of the oil lines. When you remove the nut, the flange will not come off. You need to push the oil line off of the threaded post and THEN unscrew the stud. They're all 10mm. The only way to get enough slack on the line to do this is to unbolt the oil line brackets which run along the pass side of the engine. Two torx bolts and two 8mm hex. Trust me, you need to do this and takes 5 mins. Getting this nut and stud on and off is really difficult. The other one into the back of the block isn't too bad.
Cut all of the wire ties on the back part of the engine, remove the 3 way PVC/oil rubber hose, remove metal lines in the same area. You basically need to "get stuff" out of the way so you can access the mounting (4) 10mm mounting bolts in order to remove the flange.)
Picture by Andy_TN showing some pink crust
Old and new. Shown is the driver's side that will connect to the large black coolant pipe. Make sure you have a gasket in there.
Shown is the side that will attach to the engine. Make sure that the gasket is installed and not torn as 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.
Parts
Coolant flange - (part#) 058 121 132 "w/sealing ring"
ECT - (part#) 078 919 501B
plastic clip for ECT - (part#) 032 121 142
Dummy plug - (part#) 357 121 140
also need "round seal" (part#) 903 168 02 (get three, one is used for ECT if replacing)
"sealing washer" (part#) 058 121 687
"sealing washer" (part#) 037 121 687 (that might come with flange - "sealing ring")
Tools
6 or 8 mm hex key or socket
Steps
Ok, so now that you know what the coolant flange looks like and where it connects to, it's time to get dirty. You will lose some coolant during this procedure. 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. It's also a good idea to replace the ECT as well while you are doing this.
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 if I had 6mm or 8mm hex bolts, but you need to remove two bolts that attach the coolant flange to the engine and another two that attach the flange on driver's side to the black hose.
(10mm on AWM engine)
Coolant flange partially uninstalled. It's hanging in there loose.
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 the new if needed. You hopefully have three or four O-rings depending on the flange. One O-ring goes in between the flange and the engine, the second goes between the flange and the black hose, and the other two are for the ECT and the dummy plug.
Installation is in reverse order. Make sure that when you tighten the bolts back up you just barely hand tighten them until everything is connected. Tighten them down a little bit at a time so the flange is not installed crooked. Replenish any 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.
Originally posted by BSK
