The brief
The Golf was getting on towards 120,000 km and the owner wanted the cooling system looked at before it gave trouble. That's the smart call, the water pump is a wear item, and the failure mode, an overheat, can cost a head gasket if it catches you off guard. The water pump circulates coolant through the engine and the radiator so the heat goes somewhere, and on this engine the pump and the thermostat come as one module. Over the miles the pump's bearing wears and its seal starts to weep, and the thermostat can stick, so replacing the module at the recommended mileage heads off the overheat before it happens. A proactive job rather than a roadside one.
The diagnosis
A check confirmed the cooling system was due a refresh at this mileage, the water pump module showing the early signs, a slightly rough bearing and a trace of weep, with the thermostat going along with it as part of the unit. The radiator, the hoses and the rest of the system checked out, this was preventive. So it was a water pump and thermostat module replacement, with a fresh seal, before it could fail.
The work
The cooling system was drained, the old water pump and thermostat module removed, and a new genuine VW-spec module fitted with a fresh seal and the drive belt set back up properly. The system was refilled with the correct VW coolant, the air bled out the proper way so no pockets were left, and held under pressure to confirm the seals were dry. A road test confirmed the gauge sat steady through traffic and at speed with no overheating and no noise.
The outcome
Gauge steady, no coolant loss, the engine warming up on time, and the cooling system refreshed for the next stretch. The Golf went home with the water pump sorted before it could let go. A water pump replaced at the right mileage is the proactive job that keeps the overheat from happening, far cheaper than a head gasket and a tow.