Millicent has never overheated. When the engine temperature rises, the radiator fan comes on and the temperature drops right back down.
The transmission temperature gauge does not work -- at least not properly, I think. But after four years of many long hard mountains, the fluid is still a nice clear pink. So I have stopped worrying about that.
"Your mileage may vary." I may have been lucky to get a bus in better than average condition.
If in doubt, I would probably invest in a new radiator. Expensive, but necessary. Of course, make darned sure the fan clutch works.