It started to "heat" up 3 mins before stopping.
As for mileage, 198,200 (miles).
Nope, she has never over heated, in fact she's been ruddy great in that department.
Sounds like a burst pipe then if it's going out the bottom. I'd say find that, fix it, then check (assuming it wasn't at fault) that your rad is getting nice and warm all over. Do you know when it was changed? Do you know if you have the metal water pump?