Will a stuck thermostat cause coolant to bubble out?

If a thermostat is stuck open it will cause the "bubbling". The thermostat opens and closes giving your coolant time to cool off in the radiator. When stuck open the coolant will keep circulating and just get hotter and hotter until overheating occurs. You should change it right away. I hope this will help you. If by "open" you mean that it is stuck in a position which allows coolant to constantly flow then the last answer is FALSE. If it is stuck open, and coolant constantly flows, then your engine will not heat up to the proper temperature. It will constantly be cool, because guess what, that's what coolant flow does. That means your bearings will not expand properly and such causing a host of other engine problems. If it is stuck open, then you need to replace it.