Help! Watercooling loop keeps stopping.

[tomb18]

Hi I have a loop with swiftest apogee Waterboro and fester rad.
It has been working 24/7 for the last two years. Recently, the pc shut down due to no circulation in the loop. I changed out the pump (d5 655) and all seemed well. Two days later it shut down again. I fooled around with removing air and all seemed OK. But it shut down again.
So yesterday I took the whole thing apart and the water block had a ton of crud in it. Cleaned it up, rad was clear (blow test) and all seemed good.
Today it is stopped again, and you can hardly see any flow in the rad.
What could be wrong??
Thanks

[Cue]

When you say "can hardly see any flow in the rad" what do you mean? How do you gauge the flow there? Your radiators might need flushing too. If your block had crud in it then it's likely your rad has it too. The alternative is that your flowmeter might just be busted.