C30 Engine : 1.6D - Coolant Disappears then reappears

[cwoodier]

Having an issue with coolant level. When the engine is running and the coolant system is pressurised, the level drops below minimum. Once the cap is removed and the pressure is relived the coolant level will rise back to between min and max with no coolant lost or gained.

Recently, the head gasket has been replaced along with a refurbished Cylinder head and all the usual seals and gaskets, including a new thermostat sensor, and gaskets for the housing, a new genuine Volvo expansion tank and expansion tank cap. The radiator was replaced a few months back and as of today (27th Feb 2022) the system has been completely flushed and new coolant with the appropriate mix has been added but the issue is still there.

I have tried to 'BURP' the system, however it seems there is no air lock since the car was running for 10-15minutes on idle and operating temperature with no signs of air bubbles.

The car was running perfectly when the head gasket was replaced. I had managed to travel over 700miles before a cooling pipe had burst off on a backstreet, so the engine did not overheat, in which it was quickly refitted and coolant was topped up, however, ever since that pipe blew off, this issue has always been around.

I have checked for any head gasket symptoms. There is no signs of water in the oil. I have done a combustion leak test and the results show no signs of any exhaust gas leaks and there is no contaminated coolant. I am led to believe that there is some sort of leaky or cracked pipe which is small enough to allow air into the system but for no coolant to leak out.

I am completely out of ideas with this issue. any idea what this issue could be before I book it into a garage?

[Familyman 90]

How exactly did you bleed the system? Did you use the special gizmo to extend the height of the filler neck? In what order are you opening the bleed screws?

[cwoodier]

I didn't exactly bleed it in any special way. I bled the radiator first and flushed water through the engine whilst it was idling until the liquid was clear, I then emptied tome coolant pipes and ran water through whilst it was idling. I removed and cleaned expansion tank and refitted. Once that was done I let the engine cool, topped it with coolant, turned the engine on and allowed any air to re surface.

[cwoodier]

Originally Posted by cwoodier

Having an issue with coolant level. When the engine is running and the coolant system is pressurised, the level drops below minimum. Once the cap is removed and the pressure is relived the coolant level will rise back to between min and max with no coolant lost or gained.

Recently, the head gasket has been replaced along with a refurbished Cylinder head and all the usual seals and gaskets, including a new thermostat sensor, and gaskets for the housing, a new genuine Volvo expansion tank and expansion tank cap. The radiator was replaced a few months back and as of today (27th Feb 2022) the system has been completely flushed and new coolant with the appropriate mix has been added but the issue is still there.

I have tried to 'BURP' the system, however it seems there is no air lock since the car was running for 10-15minutes on idle and operating temperature with no signs of air bubbles.

The car was running perfectly when the head gasket was replaced. I had managed to travel over 700miles before a cooling pipe had burst off on a backstreet, so the engine did not overheat, in which it was quickly refitted and coolant was topped up, however, ever since that pipe blew off, this issue has always been around.

I have checked for any head gasket symptoms. There is no signs of water in the oil. I have done a combustion leak test and the results show no signs of any exhaust gas leaks and there is no contaminated coolant. I am led to believe that there is some sort of leaky or cracked pipe which is small enough to allow air into the system but for no coolant to leak out.

I am completely out of ideas with this issue. any idea what this issue could be before I book it into a garage?

UPDATE ON THE SITUATION:

The problem has been solved. I feel like and idiot. The bleed screw on the thermostat housing was left open slightly resulting in air getting into the system. I did not know there was a bleed screw in this location since it is hidden underneath the thermostat sensor and is not visible unless it has been taken off. For anyone with the same issue, i would check this bleed screw.