You'll have to check for a leak (external or internal through engine). VW Coolant usually leaves a stain (dry pink powder) that you can spot and
follow back to its source.
Don't forget to check the inside of the vehicle (front carpets) to rule out a leaky heater core under the dash.
If you are 100% sure there are no external leaks, have the head gasket checked at a VW Shop. Coolant in the exhaust usually shows-up as white smoke
or steam. But with colder climates now, white steam (condensation) can be considered normal, especially when first starting the engine.
Common leaks on TDi engines: - water pump (coolant dripping from behind crankshaft pulley)
- thermostat flange or r-ring seal from pipe that mounts to the side of the same flange
- plastic coolant flanges at heater core fittings (at the firewall)
- reservoir cap not holding pressure
- heater core inside the vehicle
Take a close look around to see if you spot anything, once you do, post a picture here.