
I would first start by changing the thermostat as they are cheap and easy to do then the next ting I would do is pressure test the rad while cold as to loof for signs of leaks make sure that you check the rad fins for any wetbess then have a look at the rubber heater/rad hoses then check the metal cooling tubes that go to the heater core,they are noted to corrode(rust) athe sealing surfaces.since you are back there look at the water pump it has a small weap hole look to see if you can see signs of wetness ,it may also not be ciculating the coolant enough .
To look for a head leak there are several small things you can do like check the rad for oil floating in the coolant . Open the oil cap and look for a chocolate milk look to the oil ,this is most idicitive of an oil coolant passage being blown.If the combustion ring is gone it is easy to tell as if you pull all the spark plugs the one that is leaking will be much cleaner than the rest as the steam created by the piston firing and burnig off the water.The car will usually over heat in a short period of time .less athan 10 -15 minutes.
