As said before, it can only be caused by a couple of things:-
Thermostat stuck in closed position - when gauge goes up after only a few miles, stop open bonnet and feel top hose, if coldish 'stat is still closed, if red hot it's not the 'stat.
Faulty sender - You would need a thermocouple and measure water temp, with cap off it will be 100c, with cap on this rises by 1.5c per 1lb of cap pressure, so with a 10lb cap boiling point will be 115c (This is why you must NOT remove a pressure cap on a hot engine, as a normal rad' will erupt like a guyser and scald you as it suddenly boils).
Fan not cutting in:- with a really hot engine or one that's been ticking over for some time fan should run. If you short out the sender switch or stick a feed straight to the fans the temp should then fall when the fan has run for a while indicating a fan fault.
Other far less likely causes are:- A faulty water pump impellor, similar symptoms as a stuck 'stat, as water will not be circulating so engine red hot and rad' coldish.
Blocked rad:- Normally caused by not using anti-freeze all year, and adding rad repair compounds, engine & rad will be red hot. Can sometimes be cured by reverse flushing i.e. putting a garden hose in the bottom of the rad and letting water run out of the top hose connection. (Should be a problem under normal use on a vehicle of your age.
Good luck and let us know how you get on!
