only had a quick read, but what have you done with the pipe that comes from
the inlet manifold, when i had my rad in the rear if fitted a thumb bleed vent
(from a plumber's shop) found it a lot quicker to bleed the system also had 1 fitted
between the heater loop 15mm T piece with the vent soldered to the top,
just remember to remove the rubber seal b4 soldering
these with a small piece of 15mm tube between
http://www.screwfix.com/app/sfd/cat/pro.js...59&id=19155
http://www.screwfix.com/app/sfd/cat/pro.js...21&id=28307