[scooberblue]

Usually When headgasket starts to fail you can start them an leave them sat running on the drive an thay will be fine. What thay tend to do is blow threw the compression ring in the headgasket an blow into the coolant which results in either bubbling in the overflow or it pushes water out the overflow but thay only do that when there under load. It will sit running on the drive for hours fine. Either way it won’t actually overheat till the coolant level is low after it has pushed it out. Il bet pound to a pinch of salt one of your headgaskets is starting to fail unfortunately