Hi just wondering if anyone knows the answer? All of a sudden my fan comes on all the time now. I replaced the thermostat about a week latter the fan comes on whenever I turn the ignition on. Can anyone HELP?

It would be a defective temperature sensor. It's either at the thermostat housing or on the bottom of the radiator (forgot which). Turn ignition on, don't start, fan comes on. Then disconnect the temperature sender and if the fan goes off you have found the problem.

Sorry to hijack the thread, but is this the temp sensor?
http://i1170.photobucket.com/albums/r522/tylerbowen/1101121458.jpg
If it is, it helps the OP in a way. If not, sorry. :/ (This was at the bottom of the radiator, but strangely right behind that lower grill so lots of wind and stuff.)
The back of it was broken so it was hanging lower. & Closer to the hot ground. May have fallen again which would explain my engine temp increase till the fan kicks in.
Or, it could be part of the climate control outside temp sensor, boo if it's that.

Climate control outside temp sensor.

do you get a check engine light at all?

i had a similar issue with my TE the fans would turn on all of a sudden and i would get the check engine light come on. turned out to be the coolant temp sensor. the sensor is located near the radiator, just follow the top pipe going into the radiator back, your will see it go into some sort of housing with the sensor sticking into it from upwards. it should be black with a connector that can be unplugged. once you unplug it you can screw it of using a socket extension. you can buy replacement sensors on ebay for about $30:

http://www.ebay.com.au/itm/Mitsubishi-Magna-TH-TJ-TJ-Series-II-V6-3-5L-Coolant-Temperature-Sensors-/230838322477?pt=AU_Car_Parts_Accessories&hash=item35bf09452d

note: to take of/replace sensor it is recommended to drain the coolant.

Thanks for the linkage