overheating

Have you looked at your heater matrix?? or it could be a very large air lock.flush it out with ahose pipe joined to one of the top or bottom hose on the rad start the engine and just let the water push the air out also turn heater on and wait to see if that dos the trick. good luck from chris Addlestone surrey.

Have you bled the system?

if by bled you mean removed the plug at the bottom and poured water through then yes, but now it won't even start it seems to be turning over too easily as if there is no compression, any ideas??

Could be a blocked rad. so remove the rad and give it a good clean out.you say no compression.remove a spark plug and use a compression tester. in each plug hole.to see what reading you get from each plug hole,good luck from chris in Addlestone Surrey