northstar running hot

im looking into buying a 1999 sts but it is running hot im thinking it has a clogged radiator or a bad head gasket havent fulley checked out vehicle yet owner says it needs a new motor but seems to run too good for that owner is not a tech car starts first turn and runs like new any ideas thanks

Could be one of those or something as simple as a thermostat etc. etc.  Pressure test.
 
You might get a steal on this one  if the guy thinks it need a new motor, on the other hand I wouldn't jump at it without fully checking this problem out.
 
Good luck

If you have the ability to do it yourself or deep pockets I would pursue it. Worst case it will need engine. Being its a 99 check to see if recall applies you will very lucky if it does.

www.cadillacforum.com/m_18624/mpage_2/key_/tm.htm