Run it with the cap off mate to get rid of air locks, every now and again, raise the revs to about 2000RPM, keep watching for bubbles in the top of the rad. Once that stat opens, provided it isn't stuck shut, the level in the rad will drop. Keep topping it up till the rad is full, leave it running till the temp gauge sits in the middle, the heaters are hot and the bubbles stop. The leave it overnight to cool, repeat the process in the morning with the rad cap off and run it up with the cap off till warm make sure there are no bubbles in the rad filler neck.