my car 02 wrx was overheated,but after i replaced the thermostat, the guy and i noticed that the fans werent on at all, havent driven the car till 3 days ago, the fans suddenly kick back on, but today. while i was letting the car run, it overheated, and i noticed again the fans werent on ....

any ideas guys? wiring or sensor? reply fuses?

Kinda sounds like the coolant temp sensor.

Ryan

it kicked on today at normal temp. serious WTH ?? i think it just kick on sometimes

When the coolant temp sensors get old, they start to get coated and not sense the temp correctly all the time. It may work fine sometimes and not at others. That'd be the first place to start. If I recall, they're not too expensive.

Ryan

is it hard to replace?

Not really. It might be tricky to get to, but it's usually on the intake manifold I believe. Not sure where it is on the WRX.`

I doubt it's a bad CTS. There is no separate sensor for the fans, the ECU uses a single coolant temp sensor to set fueling, run the fans, and for other temp-related functions. If the sensor was that far out of range you'd notice the car running poorly, bad mileage and probably a CEL.
You may have air pockets in the cooling system, try burping the system (even if you have already done so after replacing the t-stat).

You also have a cooling fan relay that can go bad. I replaced a few as a mechanic at a honda dealership.

You also have a cooling fan relay that can go bad. I replaced a few as a mechanic at a honda dealership.

fans relay? so i just have to replace those relay fuses?