It is relatively easy to diagnose an overheating problem.
It is either insufficient water flow or insufficient cooling in the radiator.

You have to check the temperature of the water going in and coming out of the radiator.

If the engine is overheating and the water coming out of the radiator is conservable cooler than the water going in the water flow is restricted.

There are several possible causes:

• Worn water pump
• Blocked thermostat
• Blocked water channels in engine.

If the temperature of water going in and coming out of the radiator are not much different the airflow is blocked.

• A possible (probable) cause is a worn radiator is worn. Over time the airflow gets restricted and aluminium slats come loose.
• It is also possible that a worn airco condensor blocks the airflow.
• The fan only has effect at low speeds, if it only overheats when standing still or driving at low speeds is can be the fan.

The easiest way to check te temperature is with a infrared thermometer, they are not expensive.

Rob