I am so glad I found this topic ! Hopefully we can solve the puzzle together !
I imported a MK7 GTD 2016 form Germany into the Netherlands with 93.000km in march 2017. I had to refill coolant quite a few times now and noticed that this always occurs on long drives (5 hour) and sometimes on shorter drives (1 hour) and only on motorways doing 100 – 130 KM/H (60 – 75 MpH).
I could not find any leakage, no coolant on the floor of the garage. We checked the car with VCDS and not find any errors, when forced a DPF with VCDS we noticed there was coolant coming underneath the reservoir. At first I thought the reservoir would be broken so I bought a new one. The reason there is coolant coming underneath the reservoir is because there is a small overflow pipe going through the reservoir. When the pressure is over 2 BAR the coolant is released threw the pipe.
After the forced DPF and the loss of coolant I was convinced that the overpressure in the coolingsystem is related to the DPF. As I can not always drive around with a laptops and VCDS-cable I bought a blue tooth CANBUS connector and bought the app VAG DPF. This gives a dashboard with counters on the DPF process. This way I exactly know when the DPF starts and finishes.
My coolant temp on the dashboard stays 90 Celcius and my oiltemp is varying from 100 – 105.
I imported the car from a VW dealership and I still have warranty. I am allowed to let my dutch VW dealership to investigate the problem. But,……what to test or check