I had a leaky rear coolant housing, ordered a new one from RAI with all new O rings, the housing came with an O ring mounted in the flange to block and another in a separate sealed bag, but they were both the same O rings. I mounted the one from the separate bag on the right side flange with the 2 bolts, it leaked. I noticed the original seemed a little thicker, so I went to Audi with the housing and they gave me another O ring , same size as RAI, so I figured this time let me put some black RTV on it, bolted it up,let it dry overnight, still leaked, now im pissed. Does anyone know if there is a special size O ring for it, every where I go they only have American size, no metric O rings. Is this a well known leaking spot, maybe the metal tubing that goes on the flange of the housing is the problem? Also I had a blue temp sensor, figured I'd replace it while apart, they sent me a green one, called RAI, the guy said as long as the plug is the same, the color don't matter, but now my little red thermometer on the dash flashes when I run the motor, can anyone help, shed some light on this problem?

 

check your coolant temperature sensor, mine was leaking right through the center of the plug, cost me $30 in coolant for a $15 part.

 

It's new with a new O ring, and I can see it dripping from the bottom of the flange with a mirror. Did you replace your sensor with the same color?

 

Yeah i replaced blue with blue, but mine didn't come with an o ring so i had to use 2 o rings to get a good seal. On mine it looked like it was leaking from the flange but it turned out to just be running down the coolant elbow.

 

Just spoke to ECS tuning, they sent me the wrong Oring, the 2 O'rings are the same diameter but different thickness