Although OSAKA is not a good coolant but If u put any coolant in rusty radiator, or put any rusty thing in any coolant - result will be same.
To use coolant, radiator must be clean and rust free. The purpose of coolant is to protect radiator from rust - not to clean it.
To clean rust in radiator, u need to flush the radiator and then fill with normal water and then run the car for few KMs and then again flush all the water - if possible keep flushing until the clear water comes back.
Then use Liqui Moly Radiator cleaner put some water and then again drive the car for few KMs and then flush the cooling system.
Then add good anit-freez/coolant.
My radiator was also rusty even I was using coolant of Caltex then I did what I mentioned above and now after 3 months radiator is still clean.