Is it bad if the coolant bubbles in the reservoir?

A few bubbles appearing briefly? Not to worry. A steady stream of bubbles like the aerator in an aquarium tank? Houston, we have a problem! read more

Keep topping up the coolant reservoir as more air leaves the system, until the bubbles are completely gone. Thankfully, most cooling systems are designed to operate in a wide range of environments, including hot deserts, and so tend to have reserve capacity. read more

Houston, we have a problem! Even a small leak in the head gasket can allow combustion gasses from the engine cylinders into the coolant system. A steady stream of bubbles means a break near one of the cylinders, next to the coolant jacket. read more

Another more serious symptom of a bad or failing coolant reservoir is the engine overheating. If the coolant reservoir has any issue that prevents it from properly holding coolant, or from properly pressurizing the system it may cause the engine to overheat. read more

You have a leaking head gasket. Update: it has been pointed out that a cracked head might also put gas into the coolant stream. read more