What causes the engine of my Audi 80 to overheat?

I recently purchased a used Audi 80 and have noticed that the engine tends to overheat after driving for a while. The temperature gauge will start creeping up and eventually reach the red zone. What could be causing this issue and how can I fix it?

The most common cause of an overheating engine in an Audi 80 is a malfunctioning thermostat. It is responsible for regulating the flow of coolant through the engine, and if it is stuck closed, it can cause the engine to overheat.