bubbles are bad...
if your coolant is bubbling your head gasket is on the way..
IF however its being caused by the return flow from the radiator areating the coolant in the bottle thats ok.
If its any help I normally define the "bubbling" that occours when its the return coolant areating the fluid in the tank as "frothing" it looks similar to the coolant flow in an old school engine thats being run on low coolant level and the pump is cavitating.
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