wat ye think mate take right up to 120 with cap on or off then fill back up might work thanks for ye help mate more eletrical me mate if i can help with anythink mate anytime am colin any way mate
It won't go to 120 with the cap off as the coolant would've all turned to steam before that.
If you really want to get it over 102 (I can't really see why though) try taping up the front of the radiator so it can't radiate any heat out of the coolant.
As I said, I wouldn't deliberately take it over about 110 since all you seem to be trying to determine is when the fan is being triggered?
If the fan switch is not triggering by about 106 I'd be investigating the switch and the fan to see if they're actually getting power. Since it's only been a problem since you swapped the radiator (I think that's what you're saying?) you probably haven't connected something.
The simplest fix is to wire a toggle switch into the circuit and turn the fan on manually when needed - basically whenever the temp shows 100+.
Good to have a sparky on here since I'm electically challenged myself