As I see it - the main reasons for the temperature to go wild is one of the following:
- Dirt (like dandelion seeds or similar) in the cooling fins of the radiator - flush from the backside with a garden hose.
- The thermostat. (Either it's bad or someone did mount a thermostat with a higher temperature than specified, which may be useful in areas with severe winter conditions)
- The fan(s).
- Bad head gasket or cylinder head.
- Bad water pump.
- Bad temp sensor. (do a separate measurement of engine temp to figure out this one)
And also - if you have something constricting the incoming air flow to the front side of the radiator. Stuff covering the opening below the bumper can make a large difference.
Also see: http://legacygt.com/forums/showthrea...se-167523.html
A bad flow through the heater core can also cause problems.