Right i had 20xe a conversion done in my astra and left the 1.4 rad in and all was fine until it started leaking, i've now put a gsi radiator in and and the temp rises to when the fan kicks in it doesnt, we have tried changing the switches but it still does not work. the fan does work though as we bypassed it, it will go into the red and fan still doesent come on, with my old radiator it would come on at about 95degrees,
the gsi radiator i have put it does have some gunk in it near the switch end, could this be the problem?
Try giving it a really good flush through first, until the water comes out totally clear.
If still no joy, when the engine gets up to operating temperaturecarefully feel over it for cold areas. If you find any (and you may near the fan switch in your case) it's time for another rad.