Astra catastrophic loss of coolant

The only experience I have of a temperature gauge working was on an L-plate Xantia. As I was driving along the motorway a plastic bag blew onto the radiator grill. The needle climbed slowly as I drove along the motorway. I stopped at the next exit and removed the bag and the temperature fell again but the needle movement was definitely analogue, not cold, ok, and dangerous. But perhaps a Xantia doesn't count as modern?