Two problems related to coolant leaking have been reported for the 2015 Volkswagen GTI. The most recently reported issues are listed below.
2 years after purchasing my car brand new the coolant level was low. After calling the dealership they instructed me to top off the reservoir with distilled water. In February of 2019 I had the car in for general service including a coolant flush at a private, licensed, vw mechanic. He discovered my waterpump/thermostat housing was leaking and likely had been for a long time. He replaced the assembly and filled the car with new coolant. In August of 2019 I discovered once again my coolant level was low. Upon inspecting underneath my car I found dried coolant on my oil pan. My mechanic is again telling me the waterpump/thermostat housing is leaking and will need to be replaced. Nothing has been done to the cars cooling system and driving habits have not changed over the lifetime of this car. The mechanic pointed to a poorly designed seal on the thermostat housing where the leak occured. The replacement housing appeared similar in design. This is a widely reported issue, a slow coolant leak, on 2015+ vw golfs, Gtis, and rs and in extreme cases can lead to an overheated and ruined engine. The first incident occurred at roughly 60,000 miles, outside of the factory warranty. The 2nd incident occurred at roughly 88,000 miles.
Waterpump/thermostat housing covered in dry coolant, leaking due to warpage of the plastic parts used my Volkswagen. Coolant needs to be topped off every 3 months, vw said they didnt find anything wrong. Problem is getting worse as the parts fail and will lead to catastrophic failure and damage/overheating to the engine.