So your WRX takes really a long time to come up to operating temperature. Or maybe it just runs hot all the time. Chances are it's a stuck thermostat for the radiator. Don't bother replacing it with a parts-store generic 'stat, because they may not have the right hole size for proper flow. Use the factory part. You'll thank us later.
Fits all Subaru cars 2002 and newer.
Subaru Water Thermostat GasketOEM Subaru gasket for your water thermostat. Fits all 2002+ Subaru models that we know of.