Procedure
- Cold engine only. Drain via the radiator petcock into a pan, then pull the lower hose to get the rest. Save the trans cooler line routing photos on automatic cars.
- Remove fan connectors and shrouds, upper brackets, and lift the radiator out. Match the new one's fittings before going further.
- Replace the thermostat while the system is open - OEM only on Subarus; aftermarket stats are the number one cause of mystery overheating. It installs with the jiggle valve up.
- Fit new hoses with clamps positioned past the bead, spring clamps in their original orientation.
- Fill slowly with the correct coolant mix plus Subaru conditioner, nose of the car raised or on ramps - the high point matters for burping a boxer.
- Run with the cap off and heater on hot through two full fan cycles, squeezing the upper hose, topping as bubbles escape. Patience here prevents next week's head-scratching.
- New cap on, overflow to FULL, and recheck the level cold for the next three mornings.
Work at your own risk. Torque values and procedures vary by vehicle — always confirm against the factory service manual for your exact model.