not an expert but might be good start for you. Follow the hose which leads from the bottom of the radiator to the engine. There should be a a plastic manifold fitting thing. That's the thermostat housing.
The thermostat for this car is located in the water pump housing from the lower radiator hose.
Under the waterpump.
on the bottom of the water pump
You can find the thermostat in your VW on the front of the engine. You can follow the bottom radiator hose directly to the thermostat housing.
The camshaft sensor is located in the distributor. I believe you have to replace the hole distributor.
you don't
Allahu Akbar
golf gti
The thermostat is located on the front right side of the car. It is underneath where the lower radiator hose is attached to the engine.
where is vw golf gti engine number
Your thermostat is stuck closed. you will need to replace it. The thermostat controls the circulation through the radiator - when the engine heats up the thermostat is meant to switch circulation from just-engine to engine+radiator. Sounds like this isn't happening.
in the oil sump, and is chain driven