I changed the radiator fluid today and as I filled up the top fill tank I squeezed the upper rad hose like a basting bulb to get all the air out of the system Worked great.
Then I removed the overflow tank to dump the old fluid out of it and to my surpise there was a 2" layer of orange sludge at the very bottom on the overflow tank. And for the early WRX's that had the paint peeling off the inside of the radiator cap tank then you will find quite a bit of peeled paint mixed in the sludge. The sludge is quite remarkable. I wonder where it all came from?
Just FYI is all.