The brief
The Touran was losing coolant, the level dropping with a faint sweet smell and a damp patch showing up around the engine. He brought it in, which is exactly right, coolant that disappears is going somewhere and a slow leak becomes an overheat the day it lets go, which can damage the engine. Coolant, the radiator fluid that keeps the cooling system at a controlled temperature, runs around the engine through rubber and fibre-reinforced hoses, sealed with clamps. Over the years, especially on a car that's not been maintained on time, the rubber hardens, the fibre degrades, and the hoses crack and weep at the bends and clamp ends. A perished coolant hose doesn't reseal, and the leak only gets worse, so the worn hoses need replacing.
The diagnosis
A pressure test on the cooling system pinpointed it, a couple of the coolant hoses were perished and weeping, hardened and cracking, losing pressure slowly, which is the disappearing coolant. The radiator, the water pump, the expansion tank and the rest of the system held fine. That's a hose replacement, fresh hoses and new clamps where the old had perished, rather than chasing weeps that are only going to get worse.
The work
The cooling system was drained enough to get at the hoses, the perished coolant hoses removed, and new genuine VW-spec hoses fitted with new clamps, the connections checked. The system was refilled with the correct VW coolant, the air bled out the proper way so no pockets were left, and pressure tested again to confirm it held with no weep. A road test confirmed the gauge sat steady through traffic and at speed, no overheating, and the level stayed put.
The outcome
No more coolant loss, the level holding between checks, the gauge steady, the engine warming up on time, and the system holding pressure. The Touran went home with the leak resolved. Perished coolant hoses only weep worse, and the failure at the end is a sudden coolant dump and an overheat, so changing the hoses kept it to a tidy job.
