Originally Posted by ThrashZone
Crystal clear I'd rather have it than cloudy
As promised (albeit late):
Top tube is new and unused. There's some dust/debris on it as it's been on a parts shelf since 2009, but you can see it's clear.
Bottom tube is a recently retired section that has been in service since 2009. That loop was running Feser1 blue for that entire time. Never drained, never changed, only ever topped off the loop (about 10-20mL/year). Yup, I know, a HUGE no-no according to the status quo. The loop was clean as a whistle internally. Blocks, rads, pumps, res all clean and sludge free.
As you can see, after 9 years in service there is a slight coloration to the tubing. For me, I call that good.