HI,
At what temp on the temperatue gauge does the fan cut in,

normally about just above half way, sounds like the fan thermo switch
is cutting the fan in at the wrong temp, most rs turbos as std dont like
hot weather traffic conditions, have you checked your thermostat is
operating ok, and the water pump is ok, i would check the pump is
not leaking and no play in it as it could seize and chuck the cambelt off.
if all checks out, as water is coming past the radiator cap and its good
you must have pressure in the system, which suspects headgasket
maybe airlock, also check your co%, and ignition timing,
Dave,