Which engine have you got in your 19?
The later petrol engines have a water pump driven off of the cambelt.
A few questions first....
Does the cooling fan cut in at all?
Does the thermostat seem to open OK?
Is there a leak somewhere/have you had to top up the coolant recently?.
At any stage in the past,have you used any rad seal in it?
I've got a few other ideas,but check these out first.