The Volkswagen Golf IV with the 1.6-litre engine is a popular compact vehicle for Volkswagen. Its smaller sized engine means the Golf is great on gas and it can go just about anywhere; however, that small engine has a habit of overheating due to thermostat failure. If this has happened to your VW Golf then it's time to replace the thermostat. That is, unless you enjoy feeling like you have an old Volkswagen Beetle where the engine was in the back and there was no heat inside of the car to be found.
Locate the thermostat housing by tracing the top radiator hose from the radiator to the point where it connects to the engine. The metal housing that the hose connects to is on top of the intake manifold and is called the thermostat housing. Remove the two 9mm bolts that hold the housing onto the intake manifold of the VW Golf and push the housing and the radiator hose off to the side to access the thermostat.
Pull the old thermostat out of the intake manifold and replace it with a new one. The end embossed with "up" protrudes from the engine. The thermostat sits on a lip that is below the radiator fluid level inside of the intake manifold.
Pull the old thermostat gasket off of the top of the intake manifold with your fingers. The gasket may stick to the intake manifold. Use a razor blade to peel the thermostat off of the intake manifold if it is stuck.
Place a bead of RTV silicone on the surface of the intake manifold that surrounds the thermostat to create a seal that prevents leaking between the mating surfaces of the intake manifold and the thermostat housing. RTV silicone replaces the standard thermostat gasket.
Place the thermostat housing on top of the RTV silicone and bolt it back into place. Start the engine and check for leaks at the mating surfaces. Remove leaks by tightening the bolts of the thermostat housing.
Radiator fluid can reach 93.3 degrees C. The VW Golf should be cooled off for at least an hour before changing the thermostat to ensure you do not get burnt by the radiator fluid.