running a 4x4 saff cossie what?

Get a bigger IC, why oh why do you still run a standard one with a stg3 head, cam etc? what boost do you run? anything over 16psi on a standard engine is asking for trouble so think what it will be like with the mods you have!!

check easy things first off, fans kicking and switching off as normal? thermostat working fine? header tank cap sealing properly (maybe hissing noise!!) if you think you have an airlock, take the small hose off the top of the thermostat housing and run till a sollid flow of water comes out once warmed up (that's how i bleed mine and works for me)
also flush out the rad, may help a little!