update: here's a pic of the rad behind the plastic facia.
I put a bleed screw in the top of the rad to get any air out, and made doubly sure by tipping the case on it's side. I'm pretty sure it's bled.
With the facia in place and the fans at 6v, water temp is 7C warmer than air. At 12v the gradient is 6C.
Removing the fascia drops the gradient to 2C at 12V and 3C at 6v. Thus the facia is costing me about 4C.....time to mod it for better flow. Cathar was right.
The water/socket diode temp gradient is 16C. Not accurate, but a bit high. I may have to reseat and/or use something better than artic alumina.