My 1998 Sub Legacy Outback Overheats

It can't hurt to purge the air out of the system but if that does not work then back flush it again as the radiator is probably plugged up. Next time use Subaru's anti-leak or Alumaseal.

Thank you for your response.I would still like to know what a blue dye test is and what is it suppose to show.Also,what is the best way to purge the air from the system.

I'd posted a thorough procedure for purging and explaining early DOHC 2.5i motors HG issues here. Just search for it.... Note Bar's Leak NEVER helps to seal the DOHC 2.5i's infamous internal head gsaket high pressure percolation. A smaller t-stat, while not blocking flow, WILL cause overheating as its flow rate is lower. Check that t-stat was OEM. Rear heater hoses can clog...especially with a sealer. So it's important to back-flush THROUGH THE HEATER CORE; otherwise flow is too little. THEN: to purge quickly: raise FRONT of car with jacks or on curb; remove rad cap and install tight-fitting funnel in place to create a larger surface to view if possible. Start and warm up car. Add coolant mix to rad/funnel until nearly full, squeezing top hose to purge its air pockets up the funnel. Because the funnel level may be unstable it helps to turn the ac/defrost on so that the fans operate continuously, providing a measure of isothermality. Keep watching the now-stable liquid "lake" in the funnel as you twist the throttle-body to rev up and down. Be careful to not get splashed if hot coolant shoots up toward you! Either you will become satisfied that the coolant level stays stable, with NO air bubbles percolating up the funnel, or you'll see constant tiny bubbles all the time...increasing with throttle..., or you'll be satisfied that you're fully purged. If the latter, dump the funnel excess into the outer expansion bottle, cap[ the radiator, and go for a drive. IF the heater core and hoses are clear, AND the new T-stat is OE, and you still blow air (and coolant) out the radiator (and/or expansion tank), the odds are overwhelming that you need a pricey full head gasket service. Given your chariot's age, I'd toss it. But I'd only do so after ruling out the little stuff. I once "saved" a DOHC 2.5i by back-flushing coolant hoses, and a few times by returning to the proper OEM t-stat...and only a couple of times by changing out a clogged radiator, but 90+% chance your motor's percolating, and should NOT be rebuilt, as the subsequent failure rate from having overheated the block results in rod damage soonafter. Subie used this motor for only 5 years for these thermal sensitivities, simplifying things with the "new" SOHC 2.5i in 2000...which through 2009 has "external" (atmospheric...not high pressure percolation) HG leakage that although endemic, don't usually harm the sturdier block, and are just a more predictable repair. So again: flush this thing well, assure you've the right t-stat, purge, check for overheating. If so, dump the motor.