That air con electric fan doesn't really do a whole lot. Majority of your cooling comes from the vicious (clutch) fan on the front of the motor.
Easy to test viscous fan, simplest with the car OFF, try spin the fan by hand. It should stop fairly quickly. If it's keeps spinning easily then it's buggered.
Or if you are driving and the engine temp rises while idling but drops once you start moving, the fan in buggered.
I understand that funds are short for you, but the cooling system really needs some love. Having just done my own I am happy to report that I no longer have any temp issues.
You might have a few little things that are adding up to 1 big thing, over heating.
First get that copper sh!t out of the system. Clean fluid and then see what happens. Also, coolant actually does help. It raises the boiling point of water. Just grab a bottle of concentrate (5 liters) and put half in and top up with water. If you need to drop the coolant again you still have some ready to go.
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