Hello guys, i own an' 2009 Octavia VRS non-facelift, CEGA engine code, and the coolant is disappearing from the coolant tank. Sometimes i see some steam / white smoke, usually after the car warms at 90 degrees, then i turn it off for 20-30 mins. It consumes ~500ml in a month. I pressurized the system, and i didn't see any external leaks. I thought about head gasket / cylinder head. Any thoughts ? Any advice ? 

Any water contamination in the engine oil? Any coolant in the bottom engine tray or around the bottom of the radiator?

I can't see any external leaks at all, and oil doesn't seems to be contaminated with coolant