97 subaru outback 2.5- just checked the trouble codes after check engine light went on. what could be causing radiator fan problem?

Check code first,why you changed radiator?

Fix your car right away by clicking the link I attached
2011 Subaru Outback 2 5L Workshop Service Repair Manual

First thing to do is have the computer scanned for trouble codes.

thelight comes on, one or more diagnostic trouble codes (DTC) are stored in theengine control module.

If you are getting sparks at the positive cable when attaching I would suspect a hard short in the system. Check that the starter has not shorted.

Yea i would check the fusible link. Check all the wires at the alternator and to the starter. Take them loose and clean all connections. Check all body to chassis and engine to chassis/ body grounds. If they look weathered make some and replace or just add some. With the age of it you could have highly corroded wires.

sounds like one of 2 things, the thermostat or the engine has a leaking head gasket, replace the T-stat 1st, if the problem persists have the engine tested for blown head gasket(s) if the radiator was the problem u would have circulation and engine would overheat very slowly or just hotter than normal.

check the coolant level - you may have low coolant, causing the sensor to occasionally read an air pocket. If you don't correct this you will burn out your motor.
We had this problem & eventually replaced both the thermostat and radiator cap, being careful to bleed out any air pockets by running the engine form cold with the heater on hot and the radiator cap off - keep watching & topping up the coolant as the enigine heats & the thermostat opens.
Good luck!

head gasket most likely.

I've had the same problem all year. I've had four different mechanics look at this car - 97 legacy with 2.5. I've had the coolant seals replaced, the radiator cap, the thermostat, the water pump - all to no avail. I've realized now that it only overheats shortly after running sustained high rpm's. Recently the last mechanic mentioned the bleeder valve (I didn't know it had one and think maybe he didn't know either - not a subaru mechanic). Recently it overheated again (again sustained high rpm's - apparently more prone to produce air in the system), I sat the vehicle on an incline (raising the bleeder valve to be the highest point) and let the car warm up and run for half an hour. Now 300 miles and no overheat. I went through alot with this car to get to this point. Unbelievable.