The brief
The Golf had been losing coolant slowly. The owner had spotted pink coolant tracking down the front of the engine block on a quick bonnet check, and could catch a sweet smell from the bay after drives. Two clear pointers at where the leak was coming from.
Coolant tracking down the front of the block points at the water pump end. On this engine the pump is part of one module with the thermostat housing, and that assembly weeps coolant from its seals as it ages, a little every time the engine runs, which is the trail down the block and the sweet smell when it dries on something hot. It's a slow loss to start with, but a slow loss becomes a fast one, and an engine that runs out of coolant overheats.
The diagnosis
On the lift with the cooling system pressurised, the leak was traced cleanly to the water pump end of the module. The hoses, the radiator, the expansion tank and the rest of the thermostat housing all checked out clean.
Since the pump and the thermostat housing on this engine are one integrated assembly, the sensible fix is to change the module complete with fresh seals rather than try to re-seal a worn unit, so that's what got done.
The work
The cooling system was drained, the drive belt section released, and the old module removed. A new VAG-spec assembly went on, water pump and thermostat housing together, with fresh seals, and the belt set back up. Then the system was refilled with the correct 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 level held and there was nothing weeping.
The outcome
No drips, the level holding, and the sweet smell gone.
The Golf went home with the cooling system back to spec. A weeping pump module only gets worse, and the failure at the end is an overheat that can cost a head gasket, so changing the assembly on the first traces kept it to a clean job.