
This is what is inside the pipe.
Ignore the broken bit off of the flange. The flange is the "bung" you can see. I've just cut this out of my spare one because it was completely blocked. No way I could unblock it whilst inside the rad pipe. It was hard to unblock out of the pipe. It was full of solid black gunk. I am fairly certain that the one on my car is exactly the same so I would imagine that there are a lot more blocked ones out there.
The one on my car isn't causing me any problems at the moment apart from the problems I had bleeding the system a couple of years ago.
I will change it after next Fridays trackday though.
The hole in this pipe is about 3mm dia and on this one is blocked where there is a depression to allow for the angle of the flange.
Paul