I have a Astra Mk3 with C20LET+F28, air conditioning and front intercooler of a Frontera TD 2.8.
I think that the water radiator that I have now is small.
The water arrives often beyond the 100°C when the outside air has 30°C
Perhaps it is a wrong water radiator
Normally what water radiator is better to put in order not to have these temperatures?
Try and find the biggest one you can to fit in there. VMax do a huge rad but I'm not sure that will fit in an Astra and it is expensive. Deemon Tweaks sell a 'water wetter' that is supposed to drop the water temp by 15deg (F I presume). My water temp dropped from ~96 degC to 90degC by using the VMax rad and water wetter. Someone on here will be able to tell you the biggest rad that will do the job.