First, try with the old hose again to see it can fit it easily, if it does, then look at inside of the old hose fitting to see any sign of sanding or enlarging, it could be that your radiator was an after market item that it wouldn't fit the old hose and someone just sanded the old hose to make it fitted.
Other thing you can try is temporary removed the O-ring inside the new hose to see it can fit into the radiator neck, if it does fit with no problem, then you may have an incorrect radiator hose O-ring (it could happen even it's a dealer item).
If it doesn't fit with the O-ring removed, then you probably had the after market radiator with a slightly thicker diameter, indeed if this's the case then you can use a sand paper slightly and carefully sand around the radiator neck until it fits, remember to sand it a little by little and don't over sand it then lube with coolant for both radiator and hose before trying the fitting.
Note: try to do the fitting with just the radiator and without the expansion tank by turning the hose 90 degree upward.
Edit: the stuff described above applied to the hose fitting to the ET as well.
Last edited by taibinhvuong; 01-09-2013 at 06:35 PM.
Reason: Edit: The stuff aboveEdit: the stuff above applied to the fitting of the ET as well if the broiler is at the ET fitting.