What is the most common issue with the Audi 80's engine cooling system?

I am having issues with my Audi 80's engine cooling system and I want to know what the most common problem is and how I can fix it. The temperature gauge is always running hot, and I have already replaced the thermostat and radiator cap. It's a 1996 model with a 1.8L engine.

The most common issue with the Audi 80's engine cooling system is a faulty water pump. It is responsible for circulating coolant throughout the engine and if it malfunctions, it can cause overheating. I recommend getting it checked and replaced if necessary.