1. No good clean air flow to the radiator.
2. No measures to prevent hot air re-circulation.
3. Radiator highest point in cooling system leading to air locks.
It's very hard to get a rear radiator to work properly.
Have a look around this forum and also http://www.vwkd.co.uk/bb/ for more tips and help.
Yes, you are right! I´d just needed someone to get me one right track again. I was trying to save me some work. Thanks for giving me some information and by the way you project thread on "vwkd" was very helpful! Thanks!