i would add dye to the system, run it and use an ultraviolet light to pin point the leak.

assume nothing here till you find the exact leak

Roy

Good suggestion by ASEMaster6371.... just want to add something if I may.

What engine? Any oil in the Coolant Reservoir?

In general the VW engines are fairly bullet proof until they get up in miles... common leaks are, the water pump, coolant side flanges at the
cylinder head, heater core and radiators. VW Coolant usually leaves a pink residue when it leaks out, so "stains" should be visible if you look
close enough.... but a die will / can also help.

Head gaskets are usually not that common, unless high mileage or some type of major overheating had taken place. Removing the spark
plugs and checking the cylinder walls with a borescope, can show / find corrosion that is due to coolant running down the cylinder wall.

Thomas