I assume by "no thermostat" you have removed the thermostat and the coolant is free-flowing at all times.
With no restriction at the water outlet (where you removed the thermostat) the coolant moves very quickly through the system. The coolant may not be spending enough time in the radiator to actually cool down, as it is being rushed through the system. Even when open, the thermostat provides the proper amount of restriction to slow down the coolant and allow it (give it time) to cool.
I understand you have a leak in the radiator and that does need to be fixed, but you are also dealing with a slightly high coolant temp.
If it were my car, I would install the proper thermostat recommended for the car, putting the entire cooling system back to a stock configuration.