Thank you for suggestion, I still have no idea what's the reason. I'll get back here after inspection and post if anything specific is found.

I just felt like a complete fool. You see, when I had this low level coolant warning on the dashboard in the morning, I popped up hood and used torch light to see perfectly what's situation. Coolant was on the bottom of the tank. Almost empty! So, I finished work, started car and no error whatsoever. Gone to mechanic anyway, he popped up hood and coolant was barely below minimum. I couldn't believe my eyes! He topped up somewhere between 0.2-0.3 liter and I was good to go. He said it could be because it was cold in the morning, or engine pulled, or something to do with pressure. Overall, wierd experience.

Still have the same problem here, I loose coolant while driving, it doesn't really matter if I drive with high speeds or not. It seems that the pressure is too high and I'm having leaks just under the coolant tank, sometimes I loose about 200-300 ml, sometimes nothing at all, it's quite strange as it doesn't leak under the same conditions. Another thing I realized since I have this problem is that my heating system doesn't work anymore, even if I put it on 30 degrees, it's still cold in the car. 

5 hours ago, VladCor said:

Still have the same problem here, I loose coolant while driving, it doesn't really matter if I drive with high speeds or not. It seems that the pressure is too high and I'm having leaks just under the coolant tank, sometimes I loose about 200-300 ml, sometimes nothing at all, it's quite strange as it doesn't leak under the same conditions. Another thing I realized since I have this problem is that my heating system doesn't work anymore, even if I put it on 30 degrees, it's still cold in the car. 

 

Sounds to me like symptoms of the silica bag rupturing

8 hours ago, SuperbTWM said:

 

Sounds to me like symptoms of the silica bag rupturing

Does this contribute to the coolant loss or to the heating system? I also found some impurities in the coolant (fine particles), does it matter if you use G12 or G13 in the 2.0 diesel 150bhp - 2016? Because the manufacturer recommends using the G13  but my mechanic said that it's nearly the same as G12.

1 hour ago, VladCor said:

Does this contribute to the coolant loss or to the heating system? I also found some impurities in the coolant (fine particles), does it matter if you use G12 or G13 in the 2.0 diesel 150bhp - 2016? Because the manufacturer recommends using the G13  but my mechanic said that it's nearly the same as G12.

 It could explain the lack of heat as the silica beads can block up the heater matrix and the egr cooler. 
 

Also, there has been some other posts on here from other users in the past that have experienced a blocked or partially blocked egr cooler that has led to the coolant boiling when the car regenerates which can cause coolant loss through the pressure relief on the header tank cap. 
 

The latest coolant revision is G12 EVO this is backwards compatible with most modern coolants

6 minutes ago, SuperbTWM said:

 It could explain the lack of heat as the silica beads can block up the heater matrix and the egr cooler. 
 

Also, there has been some other posts on here from other users in the past that have experienced a blocked or partially blocked egr cooler that has led to the coolant boiling when the car regenerates which can cause coolant loss through the pressure relief on the header tank cap. 
 

The latest coolant revision is G12 EVO this is backwards compatible with most modern coolants

Thank you very much for the info, I'll pass that to my mechanic.

Hey guys! Got the same problem again. I started looking all over the internet, and I think I found solution. Thank you @SuperbTWM, your link guided me in right direction (idk why I ignored it at first). I'll put the link below:

 

https://forums.tdiclub.com/index.php?threads/coolant-blown-out-from-expansion-bottle.483783/page-2