I was having a coolant leak that was getting progressively worse. At first I thought it could have been the coolant return line from the heater core, but that checked out fine. The only other part that could have gone bad is the Cylinder Head Cooling Flange. I spent the two hours today taking it off, to find a big hole in the side of it. Thinking it is the culprit, and I should just order another one, I found the replacement on ecstuning, which has a small hole in it as well. The hole is not as big as the hole in my current one, but i am not curious as to why there would be a hole in a brand new one? The o-ring looks fine, but the part that connects to the engine block looks to be a bit worn down and brittle. I attached two pictures to this post, one labeled as mine, one labeled as ecs. Anyone have any ideas?

 

Well if thats where you traced the leak, its almost a 100% chance its the coolant flange leaking. They leak from everywhere on that thing, especially from the seal thats between the flange and the head. As for that hole, the one on ECS tuning looks like it has a knock out, but its still sealed, yours is flat out broken.

 

The hole is where the temp gauge goes??

 

Sorry temp sensor

 

The CTS sensor sits in the monster hole with the slat below it for the retaining clip, not where the broken off piece is.
Just buy a whole new flange, a new CTS sensor, all the O-rings and you're on your way. I would also purchase a tube of O-ring assembly lube, the O-ring between the head and flange is easy to pinch if its dry.

 

Alright, thanks. Yeah, the coolant temp sensor sits in the hole on the top side of the flange (top side while it is in the engine). I ordered the part yesterday, i'll see if I can find some of the o-ring assembly lube in the mean time.

This may warrant its own thread, but i have been going crazy trying to find information about the three relays in the engine bay ecu box? They are 373, 219 and 395. I believe the 373 is for the daytime running lights, but I have not been able to find a concrete answer for these.

 

I don't have a diagram, maybe someone with a bentley can tell ya.