My loop is clean and clear. I've flushed out my rads, blocks, res and pump. I used powdered dishwasher soap to wash out the parts. I used soft water to rinse out all the parts before reassembly. New Tubing and only distilled water. I used compressed air to blow out the rads. When new I got pieces of solder and metal shavings, but as many times as I've cleaned my rads, still no debris.
My rads do heat up and I can feel the warm air expelled out of the case. I can see good water movement in the res, so I know my rads are not clogged.
I was going to replace the cpu block. I still might.