I wouldnt replace your radiator if its not leaking just get cleaned out by a radiator shop cause most likely it will have some sort of blockage and if your thermostat is opening in boiling water it should be fine to, maybe check all your hoses for signs of detiorations while the cooling system is drained and replace them at the same time instead of filling it with new coolant and down the track having to replace a blown or leaking hose and then having to refill the cooling system with new coolant again. But i would definately be doing the pump its most likely got little to no blades left on it due to corosion