Hi guys, i have a problem again..

When my engine idling, i see bubbles popping up inside my radiator tank after i open my radiator cap.
I even encounter loss of 1/4 coolant inside my spare tank.
Is this the sign of gasket blown?

I had changed my head gasket, radiator fan, themostat, radiator cap, flush my radiator a few times n even timing belt n water pump just few months back.
Its even less than 10,000km of driving.

Is there any other causes of this?

I'm driving a Civic ek4 SiR.