Q: Bubbles and pressure in the overflow tank

If the coolant level was low due to a leak, such leaks can be found during a leak diagnostic with simple pressure testing. If the cooling system doesn’t maintain pressure, and no external leak is visible, coolant could be leaking internally. Alternatively, you can perform a chemical test for exhaust in the coolant to determine if there is a head gasket breach (although block and head cracks can cause leaks, too). If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine overheating diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.