Air in Coolant expansion tank

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.

Well if Ni$$an say its ok, and your not losing coolant and you have passed a pressure test whats the worry? Is there any coolant in the final overflow tank?

take a photo of it and post it here, ill compare it to mine but im sure a small amount will be there due to the shape of the bottle and angle of how the vehicle is sitting at certain times.

With the engine cold, remove the cap from the tank, start the engine and see if there are any bubbles in the tank. If there are none you should be OK. If you are still worried get a TK test done to see if there are any combustion gasses in your coolant.

A small air gap is normal.

Does the level in the small overflow bottle remain constant when measured cold each morning? If it drops each day you have a problem.

To bleed the air out from under the cap, I do the following:

If the outlet to the overflow tank is easily accessible, then blow softly into the outlet tube until the coolant pushes up the hose from the overflow tank and the level in the radiator rises up to the lip.

Replacing the cap with the coolant at that level, and with the overflow hose full, that should get rid of the air.

the system should self bleed but if it won't there may be a few issues that could cause problems . the car needs to warm up fully and then cool right down at which point it will suck coolant back into the pressurized bottle from the overflow bottle , although if there is not enough coolant in the overflow bottle it will just suck back air . if the tube between the pressurized and over flow bottles is split or cracked , is could be letting air in when coolant is supposed to be sucking back . i have also heard of the tube nipples on the pressurized bottle being cracked due to people leaning on them whilst working on the motor or trying to remove the hose from the bottle . the cracks could be so slight that they might not leak out coolant but will suck in air as this hose between the two bottles is not under any pressure unless you have a serious overheating event .

Also check the top seal of the radiator cap is in good nick. Sometimes they get compressed and let air in.