LOSING COOLANT AND I DONT KNOW WHY!?!?!?

[callosb6]

Hi, as the description says I'm losing coolant but seems to be when the engine is under load.
It's a 1.9 tdi pd130 with a few mods added to it.
Now I've change the header tank, thermostat, had a pressure test done, and had the system vacuumed filled back up with no signs of a leak.
The only place I can see it coming out is over flow hole in the header tank, which to me seems the headgasket or head lift when under boost.
Ive checked the oil cap for milky sludge but it is clean.
It's driving me mad now, has anyone had a similar issue?



Sent from my ELE-L09 using Tapatalk

 

[Garrett 69]

Is the radiator clear and does the fan work? How quick is the loss and how much? When was the coolant last changed? Is it still proper concentration or has it been topped up with water? It may be boiling off through the overflow?