I have a small amount of air in the pressurised top coolant expansion tank on my 2016 Patrol 3 litre CRD. Nissan says this is normal but I cannot bleed it out as when I try to remove the air it seems to come back. They say it is normal to have some air in the top coolant expansion tank (about 10-40 ml). I'm worried that even a small amount of air could mean a slight crack in the head. It doesn't loose any coolant and has passed a pressure test. I'm interested to hear what other owners think. Steve.